Unwrap produces utter randomness even with marked seams, while smart UV project kinda works

Question: I'm making an aircraft model for a game, but I'm having trouble with Unwrap on subsurf'ed parts that have had boolean cuts applied to them. I meticulously plan out nice seams using the Mark Seam function:

But it seems like the Unwrap functionality just generates a random jumbled mess of vertices without any structure:

UV smart project does kinda make sense of the unwrap, but it puts extra seams where I don't want them:

I suspect there's either a bug in Unwrap somewhere, or what I'm doing is making no sense. When I hit "Unwrap" after UV smart project, it partly redoes the UV mapping of some vertices, but stops part way through, so the UV unwrap now looks like a hybrid of the UV smart project output and the random jumbled mess of Unwrap:

Might the booleans have somehow messed up my object? I noticed it does tend to product a whole bunch of redundant and doubled vertices, but I've tried to "Remove doubles" on this already: doesn't help. "Recalculate outside" for normals: doesn't help. "Apply scale & rotation": doesn't help. Basically once I get an object into this state, nothing seems to help it anymore except to use UV smart project from this point forward and accept the imperfect UV mappings it products.
Comment: Can you share the file here: https://blend-exchange.giantcowfilms.com/? That will ease and speed the debugging process a bit..
Comment: Done: https://blend-exchange.giantcowfilms.com/b/4275/
Comment: Is there some way to gracefully resolve the messy edges?
Answer: The issue is unclean geometry left from boolean - specifically this area:

There is very thin long face running alongside the wing's trailing edge that is causing the problems. Only the top surface of the wing does not unwrap correctly, if I select other parts separately, they unwrap individually fine, so the problem is localized to that area only.
If you clean up that geometry, the model will unwrap correctly. Unfortunately removing doubles or recalculating normals won't help, it looks like some nasty leftovers from ngons.
Comment: Thanks, I believe I've figured it out. By messing around with those upper faces and placing seams carefully, I've been able to convince Blender to do the unwrap in a sensible way.
Answer: Red points in UV/image editor means that you've used Pin option.
Unpin vertex by selecting all of them in UV/image editor, then press Alt + P
After this, retry to make UV
Comment: Thanks, tried that. It now produces an absolutely bizarre unwrap, where all points fall on one line: https://i.imgur.com/N6efORW.png
Comment: Check that you unpin all vertexes, including selecting in 3d-view
Comment: I made absolutely 100% sure to do so by hitting "A" several times in the 3d view to make sure *every* vertex was selected, then proceeded to unpin it all in the UV editor.
Answer: You'll have to start the unwrapping process over and make a few tests for common errors:
1 - Edit mode > W > Remove Doubles - sometimes we create duplicated vertices by accident and they royally screw the UV
2 - Edit mode > Select evrerything you want to unwrap (or just press a until everything is lit if you want to unwrap all the mesh) > Ctrl+E > Clear Seams. This will erase any direction about where to cut the mesh in the uv
Edit mode > Select evrerything you want to unwrap (or just press a until everything is lit if you want to unwrap all the mesh) > U > Unwrap. We won't use
this unwrap, but we need to make sure it's clear
UV/image editor screen > select all > Alt+P. This will remove any pins and avoid having a pinned vertice stuck again.
After that, 3d View > Edit Mode > selection by Edges > Select the edges where you want to open the UV > Ctrl+E > Mark Seam.
After everything is nice and marked, Select all > U > Unwrap


Inverse Fourier transform Of a triangular impulse

Question: I have to find the expression of this graphic and after find the inverse Fourier transform of it. First of all I found that the expression of the graphic is $$ X(f) = \frac{1}{2} tri (\frac{f+f_0}{B}) - \frac{1}{2} tri(\frac{f-f_0}{B})$$. Now to find inverse Fourier transform , my book give me the advice to multiply numerator and denominator for i. But $$ i=e^{i \frac{\pi}{2}} $$ and $$ -i=e^{-i \frac{\pi}{2}} $$. Now I know that the Fourier transform of a triangular impulse is $$ (sinc(f)^{2}) $$ and that $$ \frac{d}{dt} tri(t) = rect ( t + \frac{1}{2}) - rect ( t - \frac{1}{2}) $$ but I don't know how to apply correctly integration property of my x(t). Thank you so much
Comment: "Segnali analogici e sistemi lineari" by Armando Vannucci , my teacher
Comment: What book is it Elena ?
Answer: It's nice to see alternative paths, like this one: First of all, properties:

Frequency shifting: $x(t)e^{j2\pi f_0 t} \longleftrightarrow X(f-f_0)$
Duality: if $x(t) \longleftrightarrow X(f)$ then $X(t) \longleftrightarrow x(-f)$

You have correctly expressed the depicted transform: $$X(f) = \frac{1}{2}\mathrm{tri}\Big(\frac{f+f_0}{B}\Big) - \frac{1}{2}\mathrm{tri}\Big(\frac{f-f_0}{B}\Big)$$
As you said, $\mathrm{tri}\Big(\frac{t}{B}\Big) \longleftrightarrow B\mathrm{sinc}^2(fB)$. From the duality property, you have $$B\mathrm{sinc}^2(tB) \longleftrightarrow \mathrm{tri}\Big(\frac{-f}{B}\Big)$$ but since $\mathrm{tri(\cdot )}$ is an even function, you can write $$B\mathrm{sinc}^2(tB) \longleftrightarrow \mathrm{tri}\Big(\frac{f}{B}\Big)$$
Now you have your FT-pair you need. If you apply the frqeuency shifting property on $\mathrm{tri}\Big(\frac{f\pm f_0}{B}\Big)$, you can easily get... what? :-) You can continue from this point.
Comment: Finally, after two hours , I obtained the correct result also with this method! And this give me the opportunity to improve with Fourier properties ! Thank you!
Answer: Hints:
X
It is quite likely that your book contains a formula (either as a solved example or as a theorem or property of Fourier transforms) that looks like
$$\mathcal F\{x(t)\sin 2\pi f_0 t\} = \frac{X(f-f_0)-X(f+f_0)}{2i}
\tag{1}$$
where $i$ is a square root of unity. So, copy the formula into your notebook, and then use the hint given in your book (multiply and divide by $i$) to arrive at
\begin{align}\frac ii\cdot\left[\frac{1}{2}\operatorname{tri}\left(\frac{f+f_0}{B}\right) - \frac{1}{2} \operatorname{tri}\left(\frac{f-f_0}{B}\right)\right]
&= i\cdot \frac{\operatorname{tri}\left(\frac{f+f_0}{B}\right)-\operatorname{tri}\left(\frac{f-f_0}{B}\right)}{2i}\\
&= -i \cdot \frac{\operatorname{tri}\left(\frac{f-f_0}{B}\right)-\operatorname{tri}\left(\frac{f+f_0}{B}\right)}{2i}.\tag{2}\end{align}
Then stare very hard at the right sides of $(1)$ and $(2)$ to see if there are any similarities that might be exploited to complete the solution.
Comment: Thank you so much !!!! I'll write it on my notebook !


Use of 掛ける vs する for 眼鏡 or サングラス

Question: Which is more common in spoken Japanese? 眼鏡【めがね】を掛ける【かける】or 眼鏡をする? I've heard both verbs used, which is why I'm curious. Would the answer be different if it's サングラス instead?
Answer: According to BCCWJ, which is a corpus based on written Japanese, 眼鏡をかける is way (> 10 times) more common than 眼鏡をする. In spoken Japanese, basic words like する tend to be used more often than in written Japanese, so the difference may be relatively smaller.
Answer:

眼鏡{めがね}を掛{か}ける or 眼鏡 {めがね}をする
If I recall correctly, they've said サングラスをします, but not 眼鏡{めがね}をします.

I think it's a very interesting observation.
I myself wear glasses, and I certainly say "眼鏡{めがね}を掛{か}ける", but I don't say "眼鏡{めがね}をする".
I don't wear sunglasses, more over I don't even have ones. If I say, I would say "サングラスをする".
I thought about this difference, and I have set up two hypotheses. There is no guarantee that they are correct.
(1) When I put on my eyeglasses, the expression "掛ける" doesn't have a nuance to make them function to correct the vision by placing them in front of my eyes, but has a nuance to hang "テンプル/ウデ/ツル hanging temples" on the ears, or a nuance to hang "パッド/鼻当{はなあ}て nose pads" on the the nose.
(2) I often ski, so when I go downhill by skiing I always wear "ゴーグル goggles".
As you know, goggles protect eyes from ultraviolet rays like sunglasses. When thinking about goggles, I notice that I say "ゴーグルを付{つ}ける" or "ゴーグルをする" instead of "ゴーグルを掛{か}ける".
Considering the difference in verbs to use, "ゴーグルを付ける" means the operation to put on them, and "ゴーグルをする" seems to pay attention to the function to protect eyes from ultraviolet rays. In the case of sunglasses, the reason that I don't use "サングラスを掛ける" but use "サングラスをする" is probably that I would focuse on proteting the eyes rather than the putting on action.
Despite the above explanation, in fact, both verbs with "掛ける" or "する" is safely used for glasses or sunglasses.
The frequency of use on the Internet is as follows.

眼鏡をかける   327,000
眼鏡をする   1,006,000
めがねをかける   48,700
めがねをする   159,000
メガネをかける 1,210,000
メガネをする  1,880,000
サングラスをかける 193,000
サングラスをする  604,000
Comment: Interesting figures. Did you get those by Googling the respective phrases? That's clever. It didn't occur to me to try that.
Comment: @Jon:  >Did you get those by Googling the respective phrases? Yes. I searched for the frequency on the Internet with keyword "眼鏡をかける"  now, then I got 376,000 hits.
Comment: @Jon You cannot rely on Google hit counts, really. It's not uncommon to see a number suddenly increasing or decreasing by 10 times. You need to use a corpus for this purpose. (So we're already seeing a sudden 20% increase for 眼鏡をかける, which is very weird.)
Comment: @mackygoo ちゃんとしたコーパスだと「サングラスをかける」が「サングラスをする」より軽く5倍以上の頻度で使われていますので、多分そのGoogle検索結果は信用しない方がいいです。ちなみにうちの環境で「眼鏡をする」だと最初「343万件」と出てその時点でmackygooさんの時と数倍違う数字ですが、4ページ目まで見ると検索結果が「39件」に変わり、それ以上表示されなくなりました(いつものことです)。
Comment: @naruto: そんなにいい加減だと信用できないですね。ありがとうございます。私は、自分の経験から判断して、眼が弱くて常時メガネを掛けている人は確実に「掛ける」と言うだろうなという自信はありますが、メガネを掛けていない人は視力矯正用メガネもサングラスも他人が掛けているのを見る機会の方が自分で掛けるより多く、その場合は、「する」ではなく、「している」と言うのかなと位に思っておりました。
Comment: @naruto Corpora are good references for how a language is written, but my question was about the spoken language. I'd agree that Google results are not definitive, but a curated corpus is not always a good substitute, either. It depends on the source material. If it's comprised of social media and forum posts then it might be useful in this case.
Answer: 眼鏡をする is not correct usage. I'd highly doubt you heard that from a native speaker. The correct verb for both is 掛ける.
する however, can be used for things worn on the head, like hats. Maybe that's what you heard?
Comment: To clarify, I'm working through Rosetta Stone right now. That's where I'm encountering the mixed usage. For hats, they teach 被る【かぶる】. If I recall correctly, they've said スングラスをします, but not 眼鏡をします. That's why I was wondering if it made a difference.

Use of 掛ける vs する for 眼鏡 or サングラス


What is the most efficient way to keep data synchronized between two locations?

Question: For example, I would like to keep a lot of music files synchronized on two different hard drives.  What is the most efficient way to do this?  The more automated the method, the better!
Comment: What is the Operation System?
Answer: rsync is pretty standard
unison is good if you want to transfer data in both directions
Comment: I use rsync at my company.
Answer: I've been using GetDropBox for some time to synchronize files across machines.  Its up and running now and runs across Windows, Mac, and Linux boxes.
Answer: You have a lot of options to do that. From simply using rSync tool to a lot of paid and free software. Here is a small list to get you started (assuming Windows OS) :
Free Versions

Syncback SE
Fling
Microsoft Synctoy
Allways Sync

Paid

Goodsync
SyncBack Pro
Answer: For a Windows system where you're wanting to do it across the internet, Live Mesh is pretty good; if you're syncing folders that are accessible from one machine (ie server to laptop) then SyncToy is a really good piece of software.
Answer: For simple syncing between multiple computers, I used to use FolderShare, which is now Windows Live Sync.  Works over a local network or the Internet, but is limited to 20,000 files per "library".  It's free.
I'm now using SugarSync, which also syncs multiple computers but in addition maintains copies of all files on their servers as well for backup and/or for accessing the files from a non-synced machine.  They've got a 45-day free trial but after that you pay based on how many gigs you're syncing.  I'm on the $100/year 60GB plan.  Because all files are necessarily synced to the cloud, it's not nearly as speedy as Live Sync if all your synced machines are on the same local network.
Answer: For Windows based systems, take a look at MirrorFolder.  We use it as a backup to the backup on some servers.  Works quite well and is very easy to use and setup.  It's not free, but it is only $40.  Good luck!
Answer: Folders Synchronizer (by softoBe) works great on my Mac.


Evolutionary Advantage to Short Humanoids

Question: Fantasy tends to have several races that are shorter than humans. With Dwarves, the size is explainable by the fact that they're usually depicted as subterranean-dwelling, and height would be a disadvantage there, but what about races like goblins, halflings, hobbits, etc.? What would provide them an advantage significant enough to allow the small size trait to become fairly universal among the race, assuming that they live above-ground?
Comment: https://en.wikipedia.org/wiki/Insular_dwarfism
Answer: You don't need an advantage, hominids start very short (~3.5 ft tall), you just need height to not be an advantage.
That said if you need them to get shorter island living organisms are often much smaller than their mainland living relatives, shortages of food, water, and space give smaller animals an advantage in surviving bad times. Island mammoths (pygmy mammoths) for instance are only as tall as humans. Resource scarcity in general can favor smaller sizes. now once they discover how to make boats they can leave the island but they will be stuck with the small size for a long time.
For climbers size can be a double edged sword as well, especially in tree dwellers, the bigger you are the fewer branches will hold you, there is a reason chimps have not gotten any bigger while humans have.
We don't see island living humans getting short now because having boats removes the constraint, and the vast majority of humans whom have ever lived in islands got their by boat. But here were early hominids which were trapped on islands by rising sea levels.
Comment: "you just need height to not be an advantage" - I think Hobbits are short in LOTR because they lack ambition; being ambitious is *not an advantage* among the hobbits. This is the same quality that indirectly permits them to carry the One Ring safely. Consider this imagery in your narrative.
Comment: So, if I want shorter humanoids, I should probably have a resources shortage in their evolutionary past and/or an island homeland?
Comment: @PhilH The OP is asking for an evolutionary reason not a magical one.
Comment: OP is looking for a reasoning to support their choice of size, so the size is a narrative device. I saw the parallel between Tolkien's use of the same and the conceptual fit. Sci fi is not some kind of vacuum for imagery.
Answer: Insular dwarfism
This is an actual term in biology and describes the decrese in median body size of a population confined to an island in comparison to a population of the same species on the mainland.
The mechanics aren't fully understood, but the availability (or scarcity) of resources like food and territory size are said to play into this. The 'breaking point' of a population is reached much earlier and smaller individuals with their reduced demand on resources have an evolutionary advantage.
Limitations of height advantages
On the other hand, taller hominids have the advantage of looking further than smaller ones to scout out resources and detect predators. Of course this only works in areas with clear lines of sight, like on a savannah. Place said population in a densely forested area and that advantage of height would be limited.
So, how to keep them short?
As said in another answer and together with this one, a rather isolated, densely forested closed region (tropical region for example) would be a good choice.
"Closed Region" could mean an island, but any structure which limits the area where the people can roam would suffice. A volcano or impact crater with limited access might be another good idea.
Are there actual real world examples?
The examples found in another answer - native people in rainforest regions, especially South East Asia - are one such example, and there is the Flores Human, which does fit the whole bill (isolated population in forested region), though the jury is still out there if it is to be regarded as a separate human species or if they had been 'just' homo sapiens with genetic defects.
Answer: When it is hot, smaller is cooler.
In environments where ambient temperature are close to body temperatures, shedding excess heat becomes a big problem for exothermic animals.  The linked Scientific American article discusses this in the context of hairlessness.
https://www.scientificamerican.com/article/the-naked-truth/

The largest terrestrial mammals—namely, elephants, rhinoceroses and
  hippopotamuses—also evolved naked skin because they are at constant
  risk of overheating. The larger an animal is, the less surface area it
  has relative to overall body mass and the harder it is for the
  creature to rid its body of excess heat. (On the flip side, mice and
  other small animals, which have a high surface-to-volume ratio, often
  struggle to retain sufficient heat.) During the Pleistocene epoch,
  which spans the time between two million and 10,000 years ago, the
  mammoths and other relatives of modern elephants and rhinoceroses were
  "woolly" because they lived in cold environments, and external
  insulation helped them conserve body heat and lower their food intake.
  But all of today's megaherbivores live in sweltering conditions, where
  a fur coat would be deadly for beasts of such immense proportions.
Human hairlessness is not an evolutionary adaptation to living
  underground or in the water—the popular embrace of the so-called
  aquatic ape hypothesis notwithstanding [see box on page 26]. Neither
  is it the result of large body size. But our bare skin is related to
  staying cool, as our superior sweating abilities suggest.

Megaherbivores were stuck with their large size for other evolutionary reasons.  But in hot Africa, in addition to hairlessness some human types also evolved small body size: the pygmies and the Khoi-San.  Consider that heat must largely be shed at the interface between body and environment.  As size increases, volume increases faster than surface area and the surface area:volume ratio decreases.  It is harder to shed heat when you are big.
So too your small humanoids: they evolved in very hot climates and smaller is cooler.  The converse is true - if you want to shed heat slowly is is better to be big than small, and larger body sizes are favored.
Answer: One way to achieve a small hominid race is to put them in a protein poor region.
Native people in rain forests, the Kalahari Desert and much of South East Asia until recently, range from being shorter than average to almost child size. Vietnamese and Indonesian males are on average 5.3ft (162cm), male Bushmen of the Kalahari Desert are an average of 5ft (152.4cm), and throughout the tropics traditional native people under 5ft are common, with the men of some tribes averaging 4.11ft (125.27cm).
When a larger diet with more protein is introduced the average height (and weight) tends to increase significantly.
So for a hominid race, having them evolve in a habitat with limited or poor protein (bugs, some fish, small animals, etc) but lots of carbs (rice, roots, grains, fruits, etc) to keep them healthy, without building up a lot of bone and muscle mass, would naturally be on the small size. If they're in a thick forest, jungle or swamp, being small would also help them crawl under the branches and vines, and climb trees where a larger body would get stuck or break the branches.
Answer: For a fantasy world, with fantasy races, any mystical explanation or creation myth will do. You don't even need to bother explaining that, if it is not important for your story setting... Many fantasy worlds such as GURPS Fantasy, Discworld, Neil Gaiman's Sandman stories, the Harry Potter series etc. have elves, gnomes and goblins of different sizes and shapes, and not one bothers to explain the reasons why they are shorter or taller or thinner or whatever.
Outside of fantasy, the average size for adults of a given species has to do with the evolutionary pressures that species has had to face in its history. There are many good reasons already in other answers, such as insular dwarfism in Anonymous's answer.
One reason I can think of, to add to the list, is that in a Fantasy setting you may expect to see a lot of epic combat, and long range warfare - facing magic, arrows, and magic arrows - is bound to be commonplace. Little people make for smaller targets. That makes you more fit to survive and breed.
Also usually among humanoids, the more magic-inclned folk tend to be very small. Only some humans are born sourcerors or become wizards, but every pixie, fairy and gnome is a natural caster. Perhaps, for humanoids, height interferes with magic. You could explain it as every humanoid having the same amount of magic energy, but the more mass you have, the less enchantment you have per kilogram of body weight. The effect of this is that along humanoid speciation, you would have a disruptive process... On one side, giants, orcs, humans etc. who rely less on magic and more on muscle. On the other hand, you have a plethora of creatures who rely on magic to survive. For those creatures, mutations that cause them to be taller are deleterious.
Answer: "Historia de gentibus septentrionalibus", a book by Olaus Magnus, a swedish writer and geographer, has been published in 1555: https://en.wikipedia.org/wiki/A_Description_of_the_Northern_Peoples .
The book contains a description of a race of pretty short people who live in Greenland. According to the book, the sky dome is located at such a low altitude over the ground in those northern lands, that only rather short people could stand and walk there at full height without hitting the sky with their heads: http://runeberg.org/olmagnus/0157.html


What is the advantage of quantum machine learning over traditional machine learning?

Question: Why exactly is machine learning on quantum computers different than classical machine learning? Is there a specific difference that allows quantum machine learning to outperform classical machine learning?
Answer: As so often, and especially in young research areas, the answer depends quite a lot on how you break down the question. Let me try a few examples:
Does quantum mechanics change what is theoretically learnable?
A beautiful paper is this reference which states a few complex results in rather clear words. Again, it depends very much on what you define as "learning". Overall, exponential speedups in the number of data samples seem to not be possible in many settings, but exponential time complexity speedups very well possible.
What asymptotic computational speedups can quantum computing provide for machine learning?
Probably the most studied approach here is to outsource linear algebra subroutines such as matrix inversion or singular value decomposition to quantum computers. These subroutines appear for example in convex optimisation used in linear regression or kernel methods.
Quantum computing research is traditionally very focused on exponential speedups, which have been claimed in many quantum machine learning papers. But they rely on lots of assumptions about how you load your data into a quantum computer, and how to process the results. The assumptions require deep technical knowledge to grasp, and it is not always clear how good classical methods are in this case. For example, the quantum algorithm may require a sparse data matrix for an exponential speedup over the vanilla classical method, but under this assumption there is another classical method that is much faster too. Some quantum algorithms have since been "de-quantised", which is a euphemism for "found to not really provide an exponential speedup if the same assumptions are imposed on classical algorithms".
Standard quantum algorithms can often give you a quadratic speedup for sampling and unstructured search problems. But classical methods are quite fast at heuristic sampling in the first place (think of contrastive divergence), and search problems so vast that a quadratic speedup does not make them tractable either.
Can quantum computations give rise to machine learning models that generalise well?
Most of the work in near-term quantum machine learning, that is QML using small and noisy devices that are the current "prototypes" of quantum computers, are interested in what models quantum computers very naturally give rise to. Do they look like neural networks? Or like anything else? Are they good generalisers? Can they be trained efficiently?
Of course, speedups are important here to - if we find a quantum model that is powerful, but easy to classically simulate, one does not need the quantum computer in the first place (still, a quantum computer may just be the fastest hardware in absolute terms to process those models, and therefore still advantageous). But much more important is to show that the quantum model generalises well.
This type of research, much driven by "variational" or "trainable" or "parametrised" quantum circuits which are optimised with the usual classical techniques of deep learning, has only few answers yet to the question of quantum advantages. There are interesting clues though - quantum models of this type are mathematically speaking linear algebra computations applied to data mapped into the very large Hilbert spaces of quantum systems. They are also modular and trainable like neural networks.
If one accepts that quantum computers are strictly speaking more powerful than classical computers, the quantum model could in principle express a larger class of functions. But how to utilise this potential advantage in a concrete quantum algorithm design is very hard to point out and not "automatically given". For example, one can show that certain ways to encode data into a quantum computer gives quantum models only access to very trivial function classes, and they are unlikely to learn anything interesting.
One reason why this is an extremely challenging (but very interesting) research area is this: if the goal is to build powerful generalisers, but the theoretical foundations of generalisation are poorly understood even in classical machine learning, and our current devices are too small and noisy to run meaningful empirical benchmarks, how can one actually show that the quantum model has an advantage? In other words, a lot of work is needed to even find a satisfying investigation framework for the question "are quantum models better machine learning models?".
So, overall I'd say like every decent research field, the art is to reformulate the question until we can answer it - at which stage the answer is usually hard to understand for non-experts.
Comment: Thanks so much for typing all that up. So, given a Quantum Support Vector Machine model and a classical Support Vector Machine model, do you suggest that there could be a quadratic speedup? Does that mean that there are certain problems that would take an unreasonable large amount of time classically but could be approached through QML algorithms?
Comment: What I meant to say is that whether a Quantum Support Vector Machine is faster than a classical SVM depends on a) what you understand a QSVM to be (there are tons of different ideas), and b) what you are trying to learn/ what data you have. But yes, in principle a quantum computer could implement something very similar to an SVM, but invert the kernel Gram matrix in linear time. And yes, most people believe the second question can be answered positive, but it is very hard to find problems useful for a broad range of applications _and_ prove that the quantum methods are better.
Comment: Thank you very much for the clarification. I realize it would be difficult to theoretically prove whether a certain problem is more efficiently computed using QML, but is there an experimental way to prove the time difference? For example, could I simply run an algorithm on a classical and quantum computer to make a judgment on efficiency?
Comment: If you want to compare absolute runtime (instead of counting the asymptotic growth of gate numbers with the input size), you can of course do that with experiments. One needs to be careful with comparisons though: to get the same precision of results to a classical computer, we need error correction, which will - once available - blow up qubit numbers and absolute runtime... Also, experiments today are necessarily small, and you may not see the advantages of the QC yet. It's tough :)
Answer: Potentially, the same advantage that quantum computing can provide over classical computing. By "quantum machine learning", in the way you seem to be using the term here, people usually refer to quantum algorithms developed to solve tasks usually handled by machine learning, that is, very roughly speaking, pattern recognition tasks (though in the quantum case algorithms aimed at performing linear algebra operations are also included in the category).
Just as there are tasks for which quantum algorithms are known to, or promise to provide enhancement over classical computers, think Grover's or Shor's, one can hope pattern recognition tasks can be similarly sped up. That's pretty much the point of quantum machine learning, also often referred to as "quantum-enhanced machine learning" in this context, to distinguish it from applications of classical machine learning to quantum information tasks, which is an entirely different field of study.
See also this question and links therein.
Comment: @RobJames sure, quantum computers can run classical algorithms, but there is no gain in doing that. That's because quantum algorithms work in fundamentally different ways than their classical counterparts. See e.g. https://quantumcomputing.stackexchange.com/a/6630/55. The advantage of quantum algorithms that provide computational speed-up over their classical counterparts is indeed that they provide computational speed-up over their classical counterparts. It is not known what tasks can be speed-up by quantum algorithms though.
Comment: Thank you very much for sharing. So essentially, let's assume that I run the exact same ML algorithm on a quantum computer and on a classical computer. Will the main benefit of running on the quantum computer be computational time? Also would this be a "quantum-enhanced machine learning algorithm"?
Comment: That makes sense. So for example, with an algorithm like QSVM (Quantum Support Vector Machines), there will be a significant computational speed-up over classical SVMs? Would QSVM be considered a "quantum-enhanced ML algorithm"?
Comment: yes, that would be one example. The field is still relatively new though, so the advantage of most algorithms comes with caveats, and not everyone agrees on whether these would be actually usable in practice. Stating the exact conditions under which a given algorithm could provide an actual practical speed-up is usually nontrivial.


How does substituting Butter for Margarine/Shortening affect the Recipe

Question: I know that Margarine / Shortening are usually softer than butter, but what other differences are there? Can I just melt the butter and call it good or will this effect my final Product? I have seen Margarine / Shortening a lot in cookies, but I am looking for a general answer.
Comment: Similar: http://cooking.stackexchange.com/questions/46464/recipe-calls-for-shortening-i-want-to-substitute-butter-do-i-need-to-melt-the
Comment: General answer: butter tastes better.
Comment: Remember that shortening is 100% fat while butter is not so they really aren't the same thing.
Answer: Here are the players:

butter (~80% fat, salt varies)
margarine (~80% fat, added salt)
vegetable oil spread (less than 80% fat, salt varies)
shortening (100% fat, no salt)

I only list it that way, because some people think a vegetable oil spread = margarine. It is not.
If you substitute an oil spread for butter, you could have problems.
My experience is that butter and true margarine can be substituted freely without negative results. Though, most people believe butter has a better flavor profile.
Salt content could also be a factor. Salt varies in different butter/margarine brands. I'm not sensitive to salt levels, but you might be.
Comment: A difference between butter and margarine (that you allude to but without specifics) is that, in the US at least, margarine is always salted, but butter comes both salted and unsalted. I mention this because for example in Hungary, neither butter nor margarine are salted. Thus, a US recipe that specifically calls for margarine may be doing so because it wants that level of saltiness, while a European recipe is more likely to call for margarine simply because butter is expensive.
Answer: The water content in butter/margarine can be enough to make things rise from steam action that you do not want risen (shortbread type doughs which you want to keep shape), or make things wet which you want to stay dry (molten chocolate)... and some textures might rely on the fat not melting below a certain temperature, or quickly going from solid to thin liquid and back  as temperature increases/decreases.
And some types of shortening are harder/more brittle than butter/margarine (thinking of eg classic Palmin here).


After effects rendering

Question: I have a small problem with rendering.When i render with default setting my video size is more than 1 GB and i was using only 10 pics, some solids and 1 null object.Can you please tell me what setting is best for rendering so that the size is reasonable and the quality is good enough.Thanks in advance.
Comment: This is entirely dependant on what version of After Effects you're using, what codecs you have installed, what the video is for, and what resolution you need it at.
Answer: As @Oliver-G said above, your final use of the footage will dictate your render settings. But I'm going to explain HOW rendering works, because it's essential knowledge.
Rendering is the process of taking your After Effects comp - a series of instructions of how to process files - and writing every pixel's value to a file (See footnote 1).
The way AE does this is to work from each layer from the bottom-most upwards, calculating expressions, effects on each later, motion etc. Then it computes the next bottom-most layer, laying it over the previously computer layer(s). The final size is not dependant on the complexity of the comp, so a still image will be the same file size (footnote 2) as a full composite with particles, effects, 3D elements etc.
Once this is done, AE then runs the resultant file through a compressor, which is where you choose your codec(s) and compression.
Codec: Every file has three (footnote 3), one for Audio, Video and Container. Think of a codec like the format for that stream in the file - so you can mix and match codecs. This is why .mov files can be unplayable on some systems: Quicktime is a Container format, and can have any of a huge number of video codecs in it.
Compression: Set how much data is "thrown away" to achieve a smaller file size. Similarly (footnote 4) to how a .zip file has a smaller size than the files it contains - fewer bits to be stored - compression can reduce the file size of a video, at the expense of quality. This is why web video - YouTube especially - looks atrocious, because it is reduced to such a small file size.
These settings are accessed through the Output Module button under each file in the Render Queue.
What you did when exporting is leave everything Uncompressed, so you had a huge file size.

Footnotes

For those with a deeper understanding of encoding, yes, I realise that keyframes, I/B frames make this statement untrue. But it's simplified for this explanation.
Not true, depending on how the codec's compression chooses to handle movement - a still image will be smaller because the codec doesn't have to record every frame of new data.
At least three, for a normal Audio+Video+Container. Multiple audio/video tracks, 3D etc. all add more codecs to the one file.
Not at all, but hey, cut me some slack :)
Answer: Try rendering it as an flv (flash video). Put the quality down to 80-90%, and your video will be much, MUCH smaller in file size with great quality. I can never get small file sizes from avi videos no matter what I do.

After effects rendering


Does Monogame on Windows Desktop use OpenGL or DirectX by default?

Question: if i use monogame 3.0 beta on windows desktop, does it use the directx renderer (sharpdx) or the opengl renderer by default?
if it uses directx is there away to make sharpdx call directly? thanks!
Answer: in the meantime i found out that it does use OpenGL for windows desktop and DirectX for windows 8 metro.
Comment: No. It's not a solution. It's your current finding but it's not the actual solution. If it's the actual solution, you'd mark it `Accepted`.
Comment: It's worth as an edit to post or as a comment
Comment: @SriHarshaChilakapati then why is there the "Answer your own question" feature?
Comment: If you had solved it before others did, you can use it.
Comment: @SriHarshaChilakapati isnt that exactly what i did?
Comment: @SriHarshaChilakapati but it does answer my question. and you cannot mark your own answer as accepted until 24h after posting it.
Answer: MonoGame currently only supports OpenGL.  It has basic support for OpenGL ES for Android/iOS, and its DirectX support is still in development and incomplete.  Hence, to answer both your questions (please don't post more than one question at a time):
It uses OpenGL by default.
There is no way to make it use DirectX at runtime, other than to recompile MonoGame in DirectX mode (which is not likely going to be usable for real projects yet).
Relevant code for MonoGame's graphics layers is at https://github.com/mono/MonoGame/tree/develop3d/MonoGame.Framework/Graphics
You will notice that DirectX support is wrapped behind conditional compilation in the code, that OpenGL assemblies are always pulled in even when compiled in DirectX mode, and that there is not even a project configuration in the .csproj that sets the necessary directives.


Reprocess mail archive for spam

Question: I have a huge archive containing some giga of mail. Once, when I didn't have Gmail, I didn't filter them for spam, so now I have massive spam into it.
Is there a way to let Gmail (or some other application) process that folder for spam, and filter all what it finds for trashing?
Comment: Which format is this archive stored in? Which OS do you want to use for the task?
Comment: they are stored on imap/gmail. windows or linux no difference.
Answer: I'm quite sure this is currently not possible from within Gmail.
You can try to sync ALL your mail with f.e. Thunderbird or Outlook and look for a way to do the trick in that program, I don't know much of these so I don't know if it's possible with them.
But I'm sure Gmail can't.
Answer: You could try POPing/IMAPing your email to an email client, using one of the various spam filter solutions.
Back in the days before I was 100% using Gmail (2008?), I was a big fan of SpamPal under Windows. But it looks now to be a dead project (although there are some recent kudos on the sourceforge page, so I think it still might work).
One caveat with many of these approaches: Effective spam filtering works (or used to!) thanks to IP black lists. As zombies are used to send spam, their IPs get flagged in the list in real time (through services like SpamCop.net and other blacklist contributors) and that's a very effective way to flag spammy mail (more effective than analyzing content, IMO). If your archive is old, the blacklist approach will work poorly, obviously because the blacklists evolve constantly (aka whack-a-mole).
Edit I agree that Gmail isn't going to work. I thought about forwarding the mails via Gmail. It probably wouldn't work, and if it would, you could possibly flag yourself for sending spam sending a giga of mail.
Answer: I would use a web based service like http://www.xeams.com/
It's 100% free with a fast set up, and you could just take all those emails and forward them to have it filter.

Reprocess mail archive for spam


What tool would you use to cut through cinder block?

Question: I have a hidden room in my house that I would like to turn into a closet. The room (currently only accessible from the outside through the vent) vents the utility room to the outside. I'm not sure why it was designed this way, other than maybe because it was easy since it was already framed for a door. Since I'm going to turn it into a closet I need to change the location of the vent. There's plenty of room between the vent and the utility room to change the location. My problem is that the outside wall is cinder block. What tool would be recommended or is best to use to cut or hammer through cinder block?
Answer: Since concrete blocks are fairly thick, I'd drill several holes along the line you want to cut with a masonry bit, then use a use a mini jack hammer such as a small DeWalt with a 1/2"  chisel bit.  The hole will not be perfect shape etc, so you will need to fill around the vent after installed with some mortar.  The pilot holes will help keep the hole in a rough shape and avoid breaking off large pieces of the block.  Even it some block breaks, you can fix it up after with the mortar mix.
Comment: They're not cheap, but watching it used on the Holmes window well episode, that thing was cutting through everything like butter.  I think this is the DeWalt version: http://www.amazon.com/DEWALT-D25899K-SDS-Demo-Hammer/dp/B0014GEY8I
Comment: Definitely not cheap, but I imagine I may be able to rent one. Thank you, I appreciate the answer, I'll look into it more.
Comment: There is a gas powered block cutting saw that you could use, but it has a 10'' blade so cutting the sides of your vent hole would not be pretty.  I would do a shirlock homes suggested just be careful either way.
Comment: Thanks lazo, I think I'm going to go the route of the mini jack hammer. I know someone that has one, so that will save me quite a bit of money.
Answer: A diamond concrete saw blade.
To do it right, you're going to need a specialized saw, possibly with water cooling.  Otherwise the blade just melts.  These blades are not cheap, so you need to protect them with a first-class water cooling system (A garden hose with a Skilsaw will not work, as you will have the additional risk of electrocution).
If you do use a dry saw you're going to need a respirator (you don't want to be inhaling that silica dust).
Comment: This was my first guess, but the more I thought about it I wondered if I was going to be able to do this myself. It will be interesting to see what I come up with. Thanks for the post.


Print Booklet feature in indesign is Shuffling my pages?

Question: Indesign has a very handy feature only id doesn't seem to be working for me. I have set up a 20 page document with facing pages (1 being the cover and 20 the back) the second page is designed to be blank, and an introduction on the third page. when I selected print booklet for a mockup it shuffled all the pages forward, so the introduction is now immediately after the cover and my back page is now set as page 18 (18- designed to be a blank page) and I have a blank page as my back page (20) and as page 19(19 was meant to be index, but printed on 17 instead). can someone help me with this? i tried to explain myself as best I could hope it isn't confusing I just don't know what I'm doing wrong.
Comment: Ive tried this and you were right my print blank pages option was  off and i ticked it and it has now worked. Thank you very much
Comment: Not sure if this can help, but when exporting a PDF with some software, you have an option to "ignore blank pages"; maybe you have this option when printing from InDesign. Make sure it's not checked.
Answer: go-meek added a comment to my question and he said to make sure when I'm in the print dialogue box, to tick the "print blank pages" option (inDesign CC) I have tried this and has worked. Thanks so make sure you set up the printer to print the actual blank pages or it will ignore your ones and add it's own.
Answer: When printing or exporting a booklet you need to make sure you set the booklet type correctly, this determines how Indesign shuffles the pages so that the end result will be correct when binding the booklet.
Comment: How do I set it up correctly please? and does that mean setting up my pages as (20,1 - 2,19 - 18,3) etc?
Comment: How are you planning on binding the booklet ? With a staple in the middle ? You should not need to re-order your pages youself, that is the function of the print booklet part. Have you tried printing the result ? it's easier to understand what indesign is doing when you have the printed booklet (or a few pages) in your hands.
Comment: Yes basic two staples in the middle. I have printed it yes after pressing print booklet and the pages moved which is my problem.
Comment: Have you printed it on physical paper, so you can hold it in your hands and lay the papers on top of each other and folded it to see the result ?
Comment: yes. I have it in my hand printed. and folded and layered and stapled and it printed wrong.


implicit declaration of functions?

Question: I'm still learning C and I understand that to get rid of most implicit declaration warnings, you add the prototype header at the beginning. But I'm confused as to what you do when you have outside methods being used in your code.
This is my code when I'm using the outside methods
    #include <stdio.h>
    #include <string.h>
    int main(void)
    {
      int arrayCapacity = 10;
      int maxCmdLength = 20;

      int A[arrayCapacity];
      int count = 0; /* how many ints stored in array A */
      char command[maxCmdLength + 1];
      int n;

      while (scanf("%s", command) != EOF)
      {

         if (strcmp(command, "insert") == 0)
         {
             scanf("%d", &n);
             insert (n, A, arrayCapacity, &count);
             printArray(A, arrayCapacity, count);
         }
         else if (strcmp(command, "delete") == 0)
         {

             scanf("%d", &n);
             delete(n,A,&count);
             printArray(A, arrayCapacity, count);

        }
        else
        {
             scanf("%d", &n);
             printArray(A, arrayCapacity, count);
        }
     }
     return 0;
    }

The methods printArray, insert, and delete are all in the form of: printArray.o, insert.o, delete.o
This is how I compiled my program: gcc -Wall insert.o delete.o printArray.o q1.c
and I get these warnings:
q1.c: In function âmainâ:
q1.c:20: warning: implicit declaration of function `insert'
q1.c:21: warning: implicit declaration of function `printArray'
q1.c:30: warning: implicit declaration of function `delete'

I've tried including this in headers but I get errors saying file or directory not found.
Any help appreciated.
Comment: What were the #include s you used and where did you put the headers?
Answer: Put them in a header file foo.h like so:
 extern void printArray(int *A, int capacity, int count);
 ...

then include that file in your source
 #include "foo.h"

Answer: You need to include the correct headers to get rid of such warnings.
If you get a "file not found" error, try to include them as
#include "myheader.h"

and put your header files in the same directory as your source code.
Generally speaking, #include "file" is for programmer-defined headers while #include <file> is or standard headers.
Answer: You should be able to just put in the function prototype at the top of the file like you do for other functions in the same file. The linker should take care of the rest.
Answer: Where did you get those .o files from? If you have written them yourself, then you should create the corresponding .h files. If you got these files from somewhere else, then you should search for the headers in the same place.
Answer: If all called functions are written before the  main() function the compiler will know their name, return type and parameter signature and can match all three of these properties with each following function invocation.
Some programmers like to write a function signature first, and do the implementation at a later time.
The only time a function declaration is essential is when using co-routines: functionA invokes functionB which in turn invokes functionA.
Done as follows:
type a(...signatureOfA...)

/* compiler now knows about a() */

type b(...signatureOfB...)
{…
// implementation of b
a(…arguments for a…);

/* compiler knows about above */
 …}

type a(...signatureOfA...)i
{…
// implementation of a
b(…arguments for b…);

/* compiler knows about above */
 …}

int main()
{
a(… arguments for a…);
/* compiler knows */
return(code);
}

implicit declaration of functions?


What is the mathematical relation between CLmax and Reynolds number?

Question: I know that Reynolds number influences CLmax, but I am not able to find any formula with which I could plot a graph!
Answer: The Reynolds number is the ratio of inertial to viscous forces, so viscous effects become smaller with a growing Reynolds number. Viscous effects cause flow separation, so a higher Reynolds number helps to delay stall.
Details depend on the particular airfoil shape, so a general formula does not exist. However, there are many plots of how maximum lift varies over their Reynolds number for groups of similar airfoils.
Below you see Figure 18 from chapter 4 of S. Hoerner's "Fluid Dynamic Lift", giving the maximum lift coefficients of some airfoils of 12% thickness. Besides the Reynolds number, nose shape and camber also influence the maximum lift coefficient, so no simple formula is possible.

Note that the Reynolds number has a logarithmic scale and shows a linear dependency with lift coefficient above Re = 10⁷. So for large Reynolds numbers you might approximate the maximum lift as something like $$c_{L_{max}} = 0.3\cdot log(Re) - 0.5$$
but there is rather little experimental data to support or refine this approximation.
Comment: Can you also give me a relation between CLmax and mach number?
Comment: Yes. With the same caveats.


What is "Fish Sauce" typically used for?

Question: A while ago I bought "Fish Sauce" for a recipe (that I've long forgotten) and ended up not using it. Now we don't know what to use it for because none of the Asian cuisine recipes we come across seems to use this stuff. It says the contents are anchovies, salt, and sugar, and it comes in a little bottle with a cap. The smell is pretty strong and fishy. What is this used for (soups, stir-fry, bbq, everything)?
Comment: I am answering this because you seem to be asking what the *role* of this ingredient is in the cuisine, rather than for a list of applications.
Comment: Protected because the question is easily misunderstood as "what *can* I use it for?"
Answer: I grew up with a Vietnamese mother that used to put fish sauce in nearly everything. While I can't exactly recommend all of her uses (she once used it in a texas beef chili -- was not good), there are a few techniques that are good to know.
A common method to create a savory sauce is to use fish sauce with sugar at a 2:1 ratio. For example, you can make Dau phu sot ca chua by sauteeing fried tofu with diced tomatoes and adding 2tbsp of fish sauce to 1tbsp of sugar. This ratio can also be used in stir-fries. I would make sure to turn on your air vents when doing this -- the smell of fish sauce hitting a hot pan is... different than what most people are used to.
It works as a savory salt alternative in a lot of dishes. I use it to season fried rice instead of using salt or soy sauce. It generally is a good idea to add this during the cooking process, so the liquid can reduce and meld with the food.
It can also be used to quick brine ground pork for savory asian dishes. I'd add somewhere in the vicinity of a tbsp per pound of ground pork. I use this technique when making Thai Krapao. There are probably other marinating/brining applications, but I don't have much personal experience with that.
You can also use fish sauce to create a wide variety of dipping sauces -- in general it is paired with something sweet (sugar or rice vinegar) to help balance out the saltiness. It is also commonly watered down (Nuoc cham) in vietnamese dipping sauces to keep it from being too overpowering.
On a personal note, my favorite use is straight up on crispy fried eggs (slightly runny yolk) over white rice. It isn't for everyone, but it's something I've been making and enjoying for years.
Comment: I believe that most Pad Thai uses a similar ratio; I think it's 1:2:3 sugar:fish-sauce:oyster-sauce.   Although, given how sugar is used in Thailand, I might have that backwards ...
Answer: Fish sauce is used as a general flavor enhancer, as it is very high in glutimates, the so called umami flavor.  As the Wikipedia article says:

In addition to being added to dishes during the cooking process, fish
  sauce is also used as a base for a dipping condiment that is prepared
  in many different ways by cooks in each country mentioned for fish,
  shrimp, pork, and chicken. In parts of southern China, it is used as
  an ingredient for soups and casseroles. Fish sauce, and its
  derivatives, impart an umami flavor to food due to their glutamate
  content.

Edit:  I should add that it is also quite salty, so it serves to contribute to the general seasoning of dishes via its salt content as well as through the glutimate content.
And as Jefromi has kindly mentioned:  fish sauce is mostly commonly used in Southeast Asia and the coastal regions of East Asia, and featured heavily in Cambodian, Philippine, Thai, and Vietnamese cuisine.  BlessedGeek points out that it is also prominent in the cuisines of  Indonesia, Laos, Malaysia and Singapore.
Comment: "featured heavily in Cambodian, Philippine, Thai, and Vietnamese" - what about Indonesia, Laos, Malaysia and Singapore?
Comment: Another relevant note from the Wikipedia article: it's common in "Southeast Asia and the coastal regions of East Asia, and featured heavily in Cambodian, Philippine, Thai, and Vietnamese cuisine." - recipes from those cultures will be more likely to include it, while I'm guessing the OP is finding mostly (possibly Americanized) Chinese recipes that are less likely to include it.
Comment: Also, there's no need to restrict its use to only Asian cuisine, I often replace some of the salt in European recipes with fish sauce, just enough give that lovely umami flavour you mention but not enough to impart any fishy flavour. The longer cooked the dish the more you can add, I find. Of course, this was common practice in Europe centuries ago with the Roman condiment garum.
Comment: That may be the case; Americanized recipes from that region are more likely to call for soy sauce, which performs much the same role.
Comment: @BlessedGeek Saying X is R does not exclude Y from also being R :-)
Comment: @Stefano I don't think any of us are saying it *restricted* to Asian cuisines, but it is not *common* or traditional by any means in other cuisines....   Agreed on the garum, of which Worcestershire sauce is the spiritual descendant.   One could in fact argue that it is Western fish sauce.
Comment: I didn't mean to imply that people were saying it was restricted to Asia just that my use case hadn't been mentioned yet; it's actually more common than you would think, especially in professional kitchens (it was a chef who worked in a French restaurant who told me about the trick).
Comment: You mentioned the soy connection ... IIRC, I heard that soy suace originated as a fish-sauce imitation / scarcity-caused-replacement.
Answer: Fish sauce is liquid drained from fermented anchovies!! When I was in Vietnam we were staying near fish sauce factories, very very smelly!!
It's used to season soups (Pho for example) and sauces and dressings (as with this Lemon Grass Beef) all over Asia. It's really very strong so best only add a little at a time!
Dipping sauce for summer rolls also nice with spring rolls
6 cloves garlic (crushed)
6 birdseye chillies (finely chopped)
50ml groundnut oil for frying
25ml cider vinegar
15ml fish sauce
100g honey
100ml water
200g salted peanuts (coarse blended)
makes A LOT of dipping sauce :)
Answer: You can use it as a salt alternative in most savoury dishes. It also a imparts a distinctive "fishy" flavour pastas and most tomato based sauces. You can also use it as a budget alternative to anchovies which is getting a bit expensive.
Answer: I just used fish sauce myself for the first time, in a stirfry. The stir fry included veggies I had in the frig (green onions, summer squash, mushrooms, snow peas) along with chicken breasts (and of course garlic and peanut oil). As soon as everything was cooked, I added fish sauce (about 1 tablespoon or two) and a couple of teaspoons of Sesame oil. It was DELICIOUS! So much better than soy sauce - I was surprised. So you CAN cook Americanized Chinese food with it. I highly recommend you try it.


A/B testing in user test

Question: I designed 4 versions of a checkout page. I want to make some user test to know which version performs better. Do you think that I have to do the tests with the same person? the big change in the interface is the layout. The informations are the same, so I'm afraid to influence the users, since they already know how the system  works (after seeing it once). Do you think that is simply better asking, which do you prefer among these 4? or I have to test the entire checkout process to see if new layouts show some problems?
Comment: Do you have a budget? Or can you say how many users you are able to test? The below answers would change a little based on your restrictions.
Answer: Should each user try all four versions?
Re-using the same user gives you the ability to statistically discriminate smaller performance differences among your versions, assuming you know the right statistics to apply (e.g., repeated-measures ANOVA, for task completion time). Re-using users allows you to factor out the users' idiosyncratic differences (as indicated by the user's average performance across all four versions), so you can focus on the remaining variability that is attributable to the differences in the versions. Re-using users can also cut costs associated with the overhead of recruiting users –in your case, to get the same amount of data, you only need to recruit one quarter of the number of users you would need if each user only tried one version.
It's legitimate to be concerned that exposure to the first version will impact performance on later versions for each user. The solution is to "counter-balance" the order of versions so different users get a different sequences of versions and the average serial position of the versions is the same across users. Ideally, you run exactly 24 users and each user gets one of the possible 24 (factorial(4)) sequences of versions. At the very least, the number of users should be an exact multiple of 4, and one quarter of the users should get have a sequence of versions of 1-2-3-4, another quarter should have 2-3-4-1, another should have 3-4-1-2, and another should have 4-1-2-3. Mix up the sequences randomly when you dole them out to users (e.g., first user gets 2-3-4-1, second gets 3-4-1-2, third gets 1-2-3-4, and fourth user gets 4-1-2-3).
Do I ask users which they prefer?
Subjective preference is only moderately correlated with objective user performance. If you want to know which version performs best objectively (e.g., least errors, minimum task time), then use an objective measure. Which version excited the users the most (or, at least, annoyed them the least) is a legitimate UX question, but different than which version was, in fact, easiest to use. You can, of course, measure both objective performance and ask users to rate the versions subjectively to capture the "full" user experience.
In either case, subjective preference may be affected by the sequence of versions you present the users, much like objective performance. Users may tend to like the first thing they see. Or maybe they like the last thing they see. I don't know.  But, more to the point, who cares? To get assured accurate averages, counter-balance the order of the versions when asking users which they prefer –just like you would for objective measures.
Do I test the entire checkout process?
Statistically, you can use a smaller sample size by focusing the task on just the things your versions vary on. This reduces the random effects from other things adding "noise" to your data that makes it harder to hear the "signal." Thus, only do as much of the task that should be affected by your different layouts. For example, if the place to enter the credit card number is the same for all versions, stop before you get to that part.
On the other hand, don't make the task be unrealistic (e.g., don't interrupt the user's flow and concentration to tell them to skip this step or that step). Also, this usability test could be an opportunity to gather data on the page in general. Maybe you can find and fix issues beyond any associated with the layout. If you have to go through a lot of trouble to recruit your users, it would be a shame to "waste" them.
Comment: I would disagree pretty strongly that the same users should see different versions.
Comment: Good summary of within-subjects experimental design. Here are a couple of references [ref1](http://vault.hanover.edu/~altermattw/methods/assets/Readings/Within_subjects.pdf) [ref2](http://faculty.uml.edu/rsiegel/47.269/TOPIC%2040A%20%20%20WITHIN%20SUBJECTS%20EXPERIMENTS.pdf) on threats to internal validity of that type of design. As the second reference says - this type of design is common in behavioral science research.
Answer: The main problem you'll run into if you just plainly ask "which do you prefer" is that it usually turns out to be preference based on fashion not function.  The reason we do test, especially usability test, is to determine which one performs best.  A test we ran that seemed to bring good results is a usability test where we had user's test on all of the interfaces, we had three, and we have them run through the same scenarios and we watch.  If your interfaces have big enough differences it will impact the results of the test.  You just need to determine if they do.  For example: Are your interfaces just an apple in different colors (that's when you ask which do you like more) or are your interfaces an apple, cat, car, and bazooka (then you run a usability test and then you can ask them their thoughts). But from my experience we ran test with 8 -12 people on 3 different interfaces that all did the same function.  It turned out well. I hope this helps.
Comment: I think you are conflating split testing with usability testing.
Answer: TL;DR Measure real-world impact (in terms of revenue, not conversion rates) using a true split test, not user preferences.
Showing all versions to a real-world user will likely result in confusion and bump up abandonment rates, regardless of the order in which you show the variations.
The way split testing works is this: come up with some variations, then split your audience and show one variation to each audience member. So, you should only be showing a given visitor version A, B, C, or D, even if they come back multiple times; it should be the same for each visit by that person, unless and until you change the design permanently.
Now, you mentioned "user testing" to figure out which variation performs best. If you have a controlled environment and can test how successfully participants complete an action for each variation, okay. But in the real world, you don't want to confuse the visitor by having a page look different every time they visit. Besides, you can't even know that a real-world user will visit that page 4 times.
And as others are pointing out, testing preferences or performance (in terms of completion) in a lab doesn't tell you anything about how a variation performs in the wild. A lab user who is told, "Here, try to checkout on this page," will try to checkout, period, because that's why they are there. A real-world user, presented with the same page, may well abandon the effort. Your lab tests will not tell you anything about how likely it is that the real-world user gives up.
Answer: I designed 4 versions of a checkout page.
Sounds like A/B/C/D testing :)
I want to make some user test to know which version performs better. Do you think that I have to do the tests with the same person?
I do, because if you look at the definition of A/B testing, it requires that there is a comparison between different versions of the same design to see which one statistically performs better.
The informations are the same, so I'm afraid to influence the users, since they already know how the system works (after seeing it once). Do you think that is simply better asking, which do you prefer among these 4?
How many users do you plan on including in the sample size? If you are doing random assignment for the testing like A/B usually requires, then different users will be introduced to different variations of the design to offset the bias.
I have to test the entire checkout process to see if new layouts show some problems?
What problems are you looking to resolve in the checkout process? You may not want to use A/B testing then, since A/B testing is generally not used to point out larger problems in the system, such as credibility or trustworthiness or help you understand why a user liked one design over another. It is primarily used to supplement other qualitative methods that help you further understand what your users want.
Answer: This is exactly what UsabilityHub was designed for. Below are some excerpts from their home page:

A/B testing in user test


What were the main doctrinal disagreements between Luther and Calvin?

Question: What were the main doctrinal disagreements between Luther and Calvin? Can anybody give an overview, please?
Comment: You know, I can't see why none of is voted this up before. This is exactly the type of supportable, non-opinion gathering question that everyone was trying to encourage a few months ago.  http://meta.christianity.stackexchange.com/questions/680/can-we-reverse-the-trend-on-low-quality-posts
Comment: I did not up-vote this question, because, while seemingly document-able, the request for an overview is essentially a request for  opinions, in this case, opinions about  opinions (of Luther and Calvin), regarding what is reliably true and trustworthy about various doctrinal beliefs. In the interest of uncovering truth, it would be more useful to request documentation, particularly scriptural references , which allow readers to judge for themselves, instead of depending upon some opinion.
Comment: @AFL - "In the interest of uncovering the truth, it would be more useful to request documentation, particularly scriptural references" - For that we have  hermeneutics.stackexchange.com , but this one is christianity.stackexchange.com . Christianity is consisted not only of the truth but also of numerous opinions about the truth. Since this site is about Christianity, it is a site for asking about the opinions that certain personalities or groups within it have held. Note that my question is not "Which one's opinion was correct?", but rather "What opinions and disagreements did they have?"
Answer: It should be noted that Luther and Calvin thought pretty highly of one another, despite their disagreements. Also keep in mind that when Luther nailed his 95 theses to the door, Calvin was less than 10 years old. It must also be remembered that a lot of what is taught under the banner of "Calvinism" today was not necessarily taught nor believed by Calvin, and the same applies to Luther and Lutheranism.
Salvation: They were both monergists, meaning they believed God completely accomplishes our salvation - human choice and deeds play no role. Luther taught the the will was bound until Christians are spiritually regenerated, and thus grace is resistible. Calvin believed that free will was gone permanently because God is completely sovereign, and thus His grace is irresistible. They essentially agreed on predestination, but Calvin believed that Christ died only for the elect ("limited atonement"), while Luther believed that Christ died for all humanity. Luther taught what is often called single predestination, which essentially means that God predestines people to heaven, but no one is predestined to damnation. Calvin on the other hand taught double predestination, that God predestines people either to heaven or hell.
Lord's Supper: Luther believed in the real presence of Christ in the Sacrament, but disagreed with the Roman Catholic doctrine of transubstantiation. Calvinists like to label this view as consubstantiation, but present-day Lutherans reject this label. Calvin affirmed the presence of the living Christ in the sacrament of the Lord's Supper by the action of the Holy Spirit, but disagreed with Luther's view because he felt it "localized" Christ to the elements. Calvin believed that Christ was "truly and efficaciously" present in the Lord's Supper, but in a spiritual sense, and through the mysterious intervention of the Holy Spirit, the communicant partakes spiritually of Christ's body" (cf. Institutes IV, 17, 18). It is argued whether Calvin's view is rightly called symbolic, or if it is a halfway point between Luther's view and the popular evangelical symbolic position. Either way, both Luther and Calvin felt that this was the biggest disagreement between them. Many Calvinists have argued that this disagreement was semantic and a result of clashing worldviews, while many Lutherans believe that these views are truly mutually exclusive.
Law/Gospel Emphasis: Calvin taught that God is absolutely sovereign, and man was created solely to bring glory to him. Luther did not necessarily disagree with this point, but his emphasis was much different. The motivation for glorifying God in Calvin's teaching was because this was man's obligation to God, which Luther felt was a Law-based focus. In Luther's teaching, while he didn't necessarily disagree with Calvin, man is privileged to serve God because of His grace and mercy, a Gospel-focused approach. This gets extended in each man's view of the Church (Calvin's emphasis of the visible vs. Luther's dual emphasis of the visible and invisible Church), but this is somewhat speculative. The Law/Gospel emphasis is a very subtle point, but most Lutherans believe it is extremely significant. Many modern-day Calvinists think this is an insignificant semantic argument (as well as with the Lord's Supper).
My Thoughts: This paragraph represents my opinion, and thus contains a Lutheran bias (I consider myself an Eastern Lutheran, which is somewhat oxymoronic). Having a Calvinist and a confessional Lutheran weigh in would be helpful to the discussion. Theology consists of a series of antinomies. They are not mere paradoxes that can be logically resolved, but both/and statements of truth. For instance,

Jesus is completely divine and yet fully human.
Jesus said "This is my body... this is my blood" and yet it is clearly bread and wine.
God is completely sovereign yet man has free will.
Christians are simultaneously sinners and saints (simul justus et peccator).
Law & Gospel (You must be perfect, but your works contribute nothing to salvation).
God is three and yet One.

Theological distinctives are often honest attempts to resolve these antinomies, but this places fallen human logic as judge over God's Word. It involves attempting to understand things that are beyond us, concepts for which our language and thinking are insufficient. Luther appeared to be more tolerant of antinomies, while Calvin often developed logical resolutions to many issues, viewing them as mere paradoxes (which only appear contradictory but can be logically resolved). In this sense, Luther was more tolerant of "mystery" while Calvin emphasized human logic more so. Both emphasized Western logic in many respects (Luther identified with Augustine's views on concupiscence which affects his belief of total depravity / original sin), but Luther vehemently attacked Aristotelian philosophy while defending Augustinian philosophy. Understanding Scholasticism and the philosophical underpinnings in German and French culture is crucial to understanding the deeper worldview issues influencing Luther and Calvin.
Overall I think both Luther and Calvin were honest, sinful men (just like the rest of us) who struggled with understanding God and His Word in their given historical and philosophical contexts. We are often unaware of our deepest biases, and this is no doubt the case for these men and for us as well. Their primary doctrinal disagreement centered in their views on the Lord's Supper, with significant philosophical underpinnings affecting this point of contention. It is my opinion that by embracing mystery and accepting the fact that our logic is fallen and corrupt, we will better "become partakers of the divine nature" (2 Peter 1:4).
Comment: As a Calvinist, I don't think it is true that "Calvin believed that free will was gone permanently because God is completely sovereign, and thus His grace is irresistible." Rather, the typical Calvinist conception of free will is that it is bound the desires of the heart, which are corrupted and captive to sin. When the heart is regenerated by God, the heart now desires good and thus chooses God. The Wikipedia article on irresistible grace is pretty good on this point and highlights differences between Calvinists and Lutherans: http://en.wikipedia.org/wiki/Irresistible_grace
Comment: Thanks for the followup, I'll bug one of my professors next week about this (I attend a Calvinist/Reformed seminary, even though I'm Eastern Orthodox - when I wrote this post I was transitioning to Orthodoxy and was torn between the two).
Comment: These are excellent points for showing us the differences between Luther and Calvin, and await more. In present theological debate, Reformed churches tend to believe that they speak for the official Protestant position on just what Protestantism is, but ignore the conflicts.
Comment: +1 for comment. May I comment also. I think this question and answer reflects somehow how I see the reality at the moment. I think my problem is how I can dare to put my trust in Jesus Christ through faith.
Comment: I don't accept the accuracy of your statement that Luther taught single predestination. See my answer to the question What is the basis for Lutheran single predestination, as opposed to double predestination?

https://christianity.stackexchange.com/q/53984/43515


Ethanol or non-Ethanol?

Question: Where I live gas is at $2.50 at 10% Ethanol at 87 octane and $2.90 for non-ethanol at 89 octane per gallon. I understand that smaller engines do not do well on ethanol. Is the loss of efficiency from containing ethanol worth the saving? Is the cost difference between the 2 either way worth the mileage and maintenance? Does smaller the engine equal less efficiency on ethanol?
Comment: What are you considering a "small engine"? To me a small engine is used on a lawnmower.
Comment: Where do you live?  As a resident of the UK I'm quite horrified!  Our pumps provide 95 octane as standard and between 97 and 99 octane performance fuel.  Race fuel (available on the pump at a small number of filling stations, usually near race tracks) is 102 octane.  Most European vehicles specify a minimum of 91 octane fuel.
Comment: The octane number in US is (MON+RON)/2 and the octane number in EU is RON. RON is higher than MON (but not by a fixed constant offset), and therefore, you can't directly compare the octane numbers in US and EU. Usually the difference is perhaps ~5-~6 units.
Comment: Where in the US do you have the option on ethanol free gasoline ( except av-gas) ?When I could still get ethanol free gasoline in some locations , I generally got 10% lower mileage with the ethanol-gas instead of the theoretical 3 % loss.
Answer: small engines don't need the extra octane and the extra octane won't produce any higher efficiency. However, non-ethanol gas doesn't attract water link ethanol gas, so it doesn't corrode the inside of the carb. That's why it's preferred. But you still need to add fuel stabilizer if you're going to keep it in the tank more than a month.
Answer: Consider this:
What costs $2.50 per gallon of E10 costs $2.50 / 0.9 = $2.7778 per gallon of actual gasoline in it.
So, if you're wondering if the smaller energy content of ethanol is an issue, don't! Even if the ethanol had actually no energy content in it, the E10 would be cheaper per unit energy.
In reality, the energy content of ethanol is perhaps around ~70% of that of gasoline. So you're paying $2.50 / (0.9 + 0.1*0.7) = $2.5773 per gallon of gasoline equivalent.
The slightly increased octane number won't even in a perfect engine that is capable of using the extra octane create much difference. Certainly it won't make the $2.90 gasoline better than the $2.50 E10 by more than the cost difference.

Ethanol or non-Ethanol?


What is the purpose of tags? How do I use them appropriately?

Question: I've created this question to address the intent and purpose of tags. There has been a lot of talk recently on the subject, and I'd like to address each aspect of tagging in one place. This is a CW, so please vote up or down each premise, feel free to comment, and add new premises at will.
Comment: This can probably be consolidated into the tag wiki for the `[tags]` tag. See: http://meta.cooking.stackexchange.com/questions/tagged?tagnames=tags&sort=info&pagesize=15
Comment: @hobodave, I'm not sure if that's the right place for it just yet. I think having a visible discussion with visible voting on the subject will help express the overall sentiment of the how tagging works; that it's not just some arbitrary ruleset but that each concept has a meaning and a hand in creating an efficient system for getting answers.
Comment: I meant once it's all said and done.
Comment: @hobodave, got it. I was a bit slow on that.
Answer: Try to choose tags that identify a single area of expertise.
Members use the "Interesting Tags" feature to highlight the questions they're most likely to be able to answer.  Some members may even subscribe to specific tags and never see any other questions.
When choosing a tag, and especially when creating a new tag, try to imagine that you're sitting in front of a panel of chefs, each with different specialties.  You don't know which chefs have which specialties, but tags help direct your questions to the right people.  The [pastries] question is for the pastry chef; the [baking] question is for the baker; the [sauce] question is for the saucier.
Common subject areas include:

Techniques - [baking], [grilling], [deep-frying], etc.
Types of food - [meat], [fruit], [bread]
Types of cuisine - [french-cuisine], [chinese-cuisine], [indian-cuisine]
Specific ingredients or foods - [chicken], [salt], [butter]
Subjects not directly about cooking but considered on-topic - [equipment], [knives], [storage]
Answer: Retagging a question should not be used as a flagging system.
Do not tag/retag a question as [delete], [off-topic], [close], etc. to indicate an action that you feel should be taken on a question.
Instead of retagging, if you do not have enough reputation to vote to close, leave your opinion in the form of a comment on the question.
If you believe that you see a serious and urgent problem (other than spam or offensive content), you can also flag the post as "Requires Moderator Attention" and write a short explanation.
Answer: Do not use tags to attempt to indicate subjectivity.
Do not tag your own question as [subjective] or [wiki] or [discussion].
If it's too subjective and argumentative or discussiony, the community will close it anyway. If it's answerable as is, the community will leave it open regardless of the subjective tag. The tag is useless.
Comment: Add `[discussion]` to this list.  Good on meta, terrible on F&C.
Comment: Is there another way to find all posts which are community-wiki?
Comment: I agree with ditching the [subjective] tag.  I'd rather treat [discussion] as a separate issue, if necessary.
Comment: @Ocaasi: Yes, there **is** a way to find community wiki posts.  Just add `wiki:1` to the query.  There are several such options; you should have a look at the [Search Options](http://cooking.stackexchange.com/search).
Comment: @Aaronut My question wasn't implying we should keep the category.
Comment: @Aaronut. If you were suggesting I'm making points without knowing how the site works, I don't think its relevant. I'm a new user like many new users, and if I have to ask a question about something, chances are others will also.  Search Options is not prominently displayed, and users will tend to use the most accessible or intuitive option.
Comment: @Ocaasi, I think he was just providing a link to the available search options. I think your enthusiasm and participation has been great so far, and with a bit deeper knowledge of how the site works, your contributions would only get better.
Comment: @Ocaasi: Can you please try to refrain from reading things in people's statements that are simply not there? You asked a question, Aaronut answered.
Comment: @Aaronut: Apparently I'm slow, but I can't figure out how to use a link like that in a comment. The normal markup just gets ignored. What am I missing
Comment: @hobodave: It's another undocumented feature.  You put the title in square brackets followed immediately by the link in parentheses.  As in: `[Example](http://example.com)`.
Answer: Pay attention to the auto-complete, and whenever possible, use an existing tag instead of creating a new one.
If you pause for a moment during or after typing a single tag, you will see a list of existing tags pop up along with their frequencies.  Choose the highest-frequency tag that is still relevant to your question.
Only create a new tag if you are absolutely certain that none of the existing tags cover the same ground.  Choosing a pre-existing tag not only helps keep the site clean, it helps get your question answered faster because people will already be subscribed to the tags you choose.
Comment: It should be said that using existing tags will result in quicker response times considering existing tags have users subscribed to them.
Comment: Is that still true once synonyms are active?  In other words, don't the synonyms "catch" any child-tags which users may have flagged before?
Comment: Excellent point @Mike, I've added that to the answer text.
Comment: @Ocaasi: Synonyms simply remap the synonym to the parent tag when the question is asked.  They don't affect searches or subscriptions (yet), and obviously they only work if the synonym has been proposed and accepted.  Expect many spurious but brand-spankin' new tags to be created that aren't covered by any synonyms.
Comment: How long until the reputation values kick up to 1500 for new tats?  Anyone with an inside track on SO developments with synonym search?
Comment: @Ocaasi: Not until the beta is over.  According to Area 51, we have 65 days remaining as of the time of writing - that puts the goal post at October 7th.
Answer: Avoid vague, ambiguous, or subjective tags.
Tags such as [easy], [cooking], or [delicious] don't help narrow down the target audience for your question.  Instead, try to choose tags that are more specific, such as [slow-cooking], or [spices].
Comment: @Ocaasi: No, no, sweet Jesus no.  This is even highlighted in the official FAQ!  **Avoid asking questions that are subjective, argumentative, or require extended discussion.**  Cooking may be a little more subjective than programming, but if a question is even *more* subjective than a cooking question ought to be, it needs to be closed, not tagged.  Anyway, what I'm referring to here is *tags that are themselves subjective*.  The issue of tags being used to indicate subjectivity is an entirely separate one.
Comment: [easy] might be better phrased [short-cuts], [cooking] is a bad tag (too general), [delicious] is a bad tag.  I would be okay with [best] if the question was about users' most successful experiences, resources, or techniques explicitly.
Comment: @Ocaasi: `[short-cuts]` is probably okay, and I don't consider it synonymous with `[easy]`.  The 1 question currently tagged `[easy]` is asking for food that's easy to make, which isn't about `[short-cuts]` at all.
Comment: `[best]`, on the other hand, is just about the *worst* tag I can conceive of.  By definition it implies a totally subjective question, and exactly zero people are going to follow that tag.
Comment: I'll save [best] for another thread.  As I've hinted at, I don't think subjectivity is toxic, so long as the question distinguishes itself as such.  There's room for subjectivity on a site filled with humans.
Comment: Ok, I won't conflate them. I agree that tags that are themselves subjective should go.
Comment: As for subjective *questions*, I'm thinking of an equivalent to "soft-questions" on MathOverflow or Math.stackexchange.  They are a separate category of questions which are generally less technical, but they are still allowed.  I think they add something to the site, and I think there is a similar function for this site, currently undefined.  This holds, provided: technical/definitive questions are the majority, and soft-questions are properly moderated.
Answer: Tags should not cross-link to indirectly-related content.
Just because you think onions and garlic are closely related, that doesn't mean you should tag a question about onions with the garlic tag.
The tag system is about users finding question that are specifically about a certain topic; it is NOT about finding questions that the asker thinks are only indirectly related. If I search for [garlic] questions, I don't want a question about onions.
Comment: I think I need to clarify , since the example you gave is certainly not what I have meant by indirectly-related content.  Tagging onions as garlic would just be silly.  Tagging both as [garden] if they were about home-growing, or [organic] if the question addressed the issue would make sense.  I think you should update this answer, so that the vote isn't on a straw-man/obviously incorrect example.
Comment: @Ocaasi: Someone sufficiently anal could tag both questions `[allium]`.  It's an indirect relationship, one that's totally valid and totally irrelevant (unless the question itself is about the entire family).
Comment: Just because some "indirectly related" tags will be unhelpful, doesn't mean all will. That's a slippery slope I never advocated.  The issue is "*usefully* related, however indirect.  If there are many questions about allium, then it's a good tag.  Otherwise not.  Case by case.
Comment: @Ocaasi: If the relationship isn't direct, it's not helpful.  I cannot conjure up a single counterexample.  If you can, you should point it out and explain it.  So far all we've heard is "some people might find it useful."  Who would follow it, and why?
Comment: The fact that there aren't many counter-examples is a good sign that there's not much practical disagreement. [Food-differences] is one potential tag.  I would use a tag to find related questions about [food-differences], same with [terminology].  I have a short-list of others, I'm going to list them in a separate post.  As for why, because I found that collection of questions to be usefully related:  it interests me.  Why wouldn't that be sufficient?
Comment: @Ocaasi, I've made this CW so you can edit the premise to clarify what you meant. I'm personally in favor of putting several tags of varying specificity on a question, if that's what you meant.
Comment: @Mike.  I edited the question to deal with the narrow case of labeling one thing as something else (which is presumed related). This still leaves open the broader kind of "indirectness", which is a meta-category such as recipe-problems, food-differences, or something like them. We probably need another answer to cover those kinds.
Answer: Use combined descriptors where appropriate
Sort of like compound words, terms might mean something specific when used together.
'brown' and 'sugar' both refer to 'brown sugar', but they're much less specific;  it's most obvious when one of the terms used is effectively useless without modifying something else ... why would I search for 'brown'?  It might refer to brown eggs, browning (process), brown butter, anything really.
Tags should be terms that you'd actually use to search for the question.
Answer: Avoid tags that describe the format of the question (as opposed to its content).
People who wish to find questions they can answer (via the tags) generally do not care whether your question is a [how-to] question, a [poll], a [definition], or a [comparison].  It is more important to them to know whether or not it's a subject they have expertise on, such as [french-cuisine] or [knives].
Comment: @Ocaasi: I really wish you'd stop trying to redefine what the Stack Exchange tag system is all about.   Tags are for people to *follow*, and nobody is going to follow random questions about `[comparison]` or `[food-differences]`.  Those are nonsense, noise tags that **zero** people will find "useful" and from now on I am going to remove every single one that I see.
Comment: @Mike: Can you explain how a `[comparisons]` tag falls outside the scope of simply linking indirectly-related content?  I mean, how is a question comparing cast iron to copper cookware in any way similar to a question comparing onions to shallots?  Why should these questions share that tag - is there really some common audience, some group of people who love to go around comparing *anything* to *anything else?*
Comment: @Aaronut, I like to look at questions that are comparing two items. I find it useful to know why I should use sea salt over regular salt. I suspect that there may be others who think that knowing how to compare two ingredients is a useful and interesting skill.
Comment: Or even a `[substitutions]` question, come to think of it.  After all, the most pertinent and possibly only *application* of such a question is to know when (if ever) you can use one in place of the other.
Comment: I think there's room for these, with proper moderation.  I'll address it specifically below, but tags are not only for question-answering, and even question-answering is not always limited to easily identifiable areas of expertise.  [how-to] is a bad tag in general, [poll] could be worthwhile, [definition] can be merged with several others about [terminology]/[classification], [comparison]/[food-differences] are a good tag and connects a distinct type of question that readers may find useful.
Comment: The StackExchange system is about it's users, at least in part.  I'm a user.  I think there is a use for tags which exceeds what you have described.  Importantly, *I* would use tags this way.  I doubt I'm the only one.

I still propose that [Food-differences] is useful because it helps collect areas of common confusion regarding terminology: I am interested in this, plus, I might seek to help readers by clarifying their confusion in this area.
Comment: Perhaps this is not an ideological or software-purpose issue so much as a pragmatic one.  I'm not suggesting all meta-tags are good, only select useful ones.  Just like some "direct" tags aren't great.  That's my only criterion for a tag: is it useful for readers, askers, or answerers. And secondarily, how can it be implemented most efficiently.
Comment: I've downvoted this because I personally also find [comparisons] to be useful and interesting.
Comment: Just to clarify, is a downvote support of the answer itself or of the type of tag mentioned in it.  I mention it, since these answers are negatively phrased, so a downvote would be *in support* of the tag.
Comment: @aaronut, after thinking about this one long and hard, maybe I'm wrong. I'm having trouble convincing myself that [comparisons] is different from something like [recipe-problems]. Because of that, I've removed my downvote.
Comment: Thanks @Mike.  It's not that I don't think comparisons are useful, or even that somebody wouldn't enjoy comparison questions.  It's more that I think the "comparison" aspect is largely incidental, and the question could easily be reworded as "When should I use sea salt instead of table salt?" which wouldn't be a comparison at all (but would be just as useful and probably get the same kinds of answers).  Now that I have a clear head myself, I would assert that `[comparisons]`, at least in terms of foods, is basically a particularly nebulous superset of `[ingredient-selection]`.
Answer: Don't be overly specific.
If the tag has never been used before, and there isn't a good alternative tag, consider if it might be too specific, and you need to be more general.
As a specific example, there's currently a tag for infrared-thermometers.  Would thermometer be specific enough, or is even that too specific and gadgets be general enough?  Or should it all be filed under equipment?
If there's only one item in a category and there is unlikely to be more additions, it's functionally useless as it can't be used to find similar items (or for people to filter to avoid similar items)
Comment: This is good advice so long as it's taken in context.  The evaluation cannot only be backward-looking.  I think the key question is, "in a few years, once the site has grown considerably, will this category have enough entries to be useful by itself; or, would the broader category be too crowded to be usefully searched/disambiguated.
Answer: Avoid terms with more than one meaning.
eg, the tag [seasoning] has been used for both seasoning cast iron pans, and seasoning food.
[orange] might refer to the color orange, or the fruit.  (but it was used to refer to the general flavor of oranes)
[coriander] means a different thing if you're American from other english-speaking countries.
If this were a thesaurus, we'd qualify the terms: 'orange (fruit)' vs. 'orange (flavor)'.  We can solve this particular problem by using the plural for the fruit, so we can be fairly certain it's not talking about the color.  The closest alternative is to use a precombined descriptor -- I've changed the 'orange' flavor item to `[orange-flavor]'.


How can I get rid of unwanted visitors?

Question: In Animal Crossing: New Leaf, a character has been hanging out in the shopping district for a few days. She has never lived here, there is no campsite available and she is not a specialty character. Will she ever leave?
Comment: Can you post a screenshot? Believe it or not it may be a shop owner or resident.
Comment: Or, at the very least, the name of the NPC?
Answer: In Animal Crossing: New Leaf, the game stores 16 different non-residing villager characters. These stored characters will show up in the shopping district area, stores, etc. Usually, these stored characters are all past residents of your own town, but occasionally you can pick up the character information from another town you've connected to. Rarely, they can be characters randomly chosen to wander your game.
Will these wandering animals ever leave? So like I said, the game stores 16 characters. 16 unique characters. This means you can rotate her out of the stored characters by allowing current villagers to move, eventually bumping out the unwanted character.
I've used this technique to get back one of my favorite villagers, who accidently moved out. Villagers that are on this 16 character list will not move back into your town. I bumped him out of the 16 (basically out of the game's memory of the character) so I could adopt him from a friend's town when he was in boxes.
The game has this weird system to make the in-game relationships more realistic. How weird would it be if a villager moved out your best friend and moved back in 3 days later, introducing themselves like they've never met you?

How can I get rid of unwanted visitors?