What is the significance of the game "Monument Valley" to House of Cards plot

Question: I don't understand how the game "Monument Valley" played a role in Frank's plan putting a "philosophy" behind his AmWorks program. When he started typing on the keyboard and showing the screen to his subordinates, it was not revealed what was in that game the he saw useful. I never played the Monument Valley, I just read that it's a puzzle game. So can anyone shed some light on this?
Comment: I have played this game, and it requires a bit of out-of-the-box thinking to solve some problems. You may have to move walls, stairways, and walkways, (sometimes as a precursor) to allow your character through doors, passageways, and along cliffs. In other words, you have to be able to think many moves ahead. Sometimes you have to not only SEE the angles, but MAKE a few of your own - true politician-style.
Comment: As stated it was the *review* of the game that was key to the plot. However, I imagine TV and cultural critics in the future will have fun using the game itself for all sorts of metaphors to describe Frank's manipulation of the white house.
Answer: Tom Yates, a very famous author dedicated with many prizes, wrote a colorful review of the princess game Monument Valley. The whole review reads as follows (Frank reads it to Yates when they first met):

Whoever you are, whoever you think you are, believe that you're also a silent princess. Your name is Ida. Your journey is one through a forgotten landscape of twisting staircases and morphing castles, atop floating stones defiantly crossing an angry sea, within dimly-lit caverns cobwebbed with ruins M.C. Escher could only grasp at in a dream state.

Altough Frank was used to play action games (I think, it was Halo?) in the first seasons, he is seen playing Monument Valley on his tablet (S03E05, after about 15 minutes), which seems to be far away from his normal taste in games. Later, he shows the review for this game to Remy and Seth in order to convince them that someone (Yates) who can write reviews with such a colorful language and which are so famous are perfect to write a book about the philosphy of AmWorks.
He tells Yates (middle of S03E05) that his review was the reason he tried this game:

I tend to play shoot-'em-ups.
  The indie games don't really interest me.
  I need adrenaline and action.
  But when I read this, I had to try it.
Comment: Sorry - that he mentions at some point that the review is the reason he tried the game in the first place.
Comment: @RodrigoGómez You are right! I rewatched the scene and will add it to my answer.
Comment: He was playing Killzone 3 on a PS3.
Comment: @Lilienthal yes, I know, But I didn't find a way to edit it using the SE iOS app. I have just deleted the first incomplete comment, I'll try editing the other on the computer directly.
Answer: It wasn't the game that mattered, but its review, written by Tom Yates:

Having read Yates' effusive review of Monument Valley, President Frank Underwood, longtime fan of shoot-'em-up video games, was so intrigued by its flowery language that it made him depart from his usual video game tastes and give the indie game a try. The occurrence made Underwood decide to look Yates up and commission him to come up with a piece of non-fiction political literature on the America Works, thinking that such a work would inject the public perception of his jobs program with some positivity.
Answer: In addition to these plot related answers, I'd add that there is a significant amount of product placement in the show itself.
One particular egregious point that sticks out for me is in Season 2 when Frank Underwood goes over to Peter Rousseau's and sees Rousseau's son's Playstation Vita, which is very poorly performing
<code> Underwood: "Is that a PS Vita? Which games does he have?"
 Rousseau:  "All of them."
 Underwood: "I have a console at home I play sometimes to relax.
             I oughta get one of these for the car."
</code>
There are a number of other really heavy offenders, but if you give it some thought while watching the show they become really hard to miss.
The show does not list any disclosures for product placements and states that products like the Vita are used "with permission." Additionally, according to the LA Times, a spokesperson from Netflix says they don't have any product placement deals in place. I don't personally find that believable myself.
http://articles.latimes.com/2013/may/03/entertainment/la-et-st-house-of-cards-netflix-product-placement-20130503
Comment: Wow, Neftlix says no product placement? As if the mention of Playstation Vita served any other purpose...


Build a table with columns of raster values from multiple raster datasets, using Python, GDAL, or PyQGIS?

Question: I have a series of raster datasets, clipped to the same extent, with matching cell resolutions, each of which represent land surface temperatures (LST) captured by the MODIS sensor.  Each raster stores LST values for sequential time intervals (daily or 8-day intervals) for a year.
I need to build a table with the following specifications:

each row represents a grid cell
one column with a unique grid cell ID
each subsequent column stores LST values from rasters for each time interval (so up to 365 columns max.)

I realize I could do this easily with ArcPy by creating grid cell centroids from one of the rasters, then use the Multi Value to Point tool to build an attribute table for the resulting point dataset with a field for each LST raster.  However, I am building this tool as a PyQGIS plugin, and so need to do this with FOSS libraries and resources (i.e. GDAL/OGR, PyQGIS, etc.)
At this point, I'm a bit unsure as to the best method for doing this.  Here are the alternative methods I've considered:

Convert all of the rasters to xyz files, then use Python's built-in csv library to merge the xyz files together.  I like this option, but I'm still a Python novice, and I haven't been able to figure out how to iteratively merge csv columns together.
Create a point shapefile from grid cell centroids, then try to incorprate Borys Jurgiel's Point sampling tool plugin to extract the values from all of the remaining rasters.  This tool is written as a plugin however, and would take quite a bit of work to fit into my existing code.
Turn the XYZ value into a 1-D Numpy array, and do some kind of Numpy-related magic? (I'm not very experienced with Numpy at this point...)
Use a RDBMS and SQL to do a relational join between csv files.  I'm familiar with PostGIS and SpatiaLite/SQLite, but this will eventually be part of a QGIS plugin, so I'd raster not force users to have to install an RDBMS just to fulfill this one task in my workflow.

Are there any other suggestions as to how I should attack this?  The first option (joining csv files) seems like the best, but maybe I'm over thinking this problem.
UPDATE
Just to follow up on this issue, I decided to go with option 1.  I convert all of the rasters to xyz file, using gdal2xyz.py (included with standard GDAL installations), then I add a header row and unique id column for each xyz file (stored as a CSV).  The final solution to merge these files together into a single CSV table can be found at StackOverflow, here.
Comment: @2 you cannot use shape files if the number of columns is above 255.
Comment: That's a good point about the shapefile.  That pretty much negates option 2. Thanks!
Answer: Your first idea seems to me good. I would use cut and paste Linux command and a bash script on Linux and gdal to convert raster to sorted ASCII gridded xyz file.
If you would like to use Python use Pandas to handle csv files.
Comment: Thanks for the comment.  Pandas do seem to be an easier way to do csv manipulation.  I'm trying to stay away from too many third party libraries (outside of what's available with through OSGeo4W).


What would a human need to have a better chance at surviving a very long fall?

Question: I am currently writing a book about people with powers. One of these characters have a power to make portals, and I am wondering what would make it realistic
for said character to survive hitting the floor with a lot of momentum. (You can bend reality a little, it is a book!)
Comment: If they can portal, then portal *upside down* so they suddenly are falling upwards instead of downwards. At the top of the arc, vertical velocity zero, portal again to to the ground, a nice cafe, sit down, and reflect how useful all that high school physics was.
Comment: A nice thick jelly-bed. Or perhaps a swimming pool. Or the backyard trampoline. Alternately, if the character the main antagonist, then they will survive until the final conflict regardless of the surface - a henchman or white cat will take the, ahem, fall.
Comment: Can you describe your "power" system a bit more? Does this person only have the mentioned portal power, or do they have additional minor powers along side the one major one?  Are there any trade-offs that should be mentioned?
Comment: The character was engineered by scientists so there could be minor powers to help with the main power.
Comment: What about [things attachet to her feet to somehow absorb the shock](https://i1.theportalwiki.net/img/thumb/8/81/Portal_Chell.png/166px-Portal_Chell.png)? Worked for Chell in *Portal*.
Comment: How far down is the floor?   Why can't he make his portals at ground level?
Comment: He can make portals wherever he can see so as long as he can see it he can make a portal there but I was playing with the idea of some weird shoes/boots.
Answer: There's a YouTube channel called Today I Found Out that occasionally asks and answers questions like this, and they recently did one on falling out of an airplane without a parachute.
And the answer to the question of what you need for a fall at terminal velocity to be at least theoretically survivable turns out to be:  'Not a whole lot.'  At terminal velocity, stretching out the distance you decelerate over about a meter is enough to turn your odds from 'certain to pancake' to 'broken bones and a hospital, if you're lucky'; it's just a matter of finding a way to get that extra meter or two to slow down.
People who have historically fallen out of airplanes and survived usually did so because they were still in their chair, and the chair hit something on the way down that caused it to slow gradually rather than instantly.  For instance, one person survived because they hit a snow-covered slope, going in mostly the same direction they were, so they slid for a while.  Another survived because their chair went through a dense jungle canopy, and the branches bled off a lot of the speed.  Of course, neither one of those people would have survived if the chair wasn't there to take the hit, so you may need to get a little creative.
Comment: I'm frankly shocked the old "hit all the branches on the way down" chestnut actually has some basis in reality.
Comment: There's one out of WWII where the guy appears to have been uninjured (uncertain as he was injured when he jumped.)  Unfortunately, we don't know how he landed as he blacked out on the way down and woke up on the ground.  Being wartime nobody investigated in much detail.  Suspicion is snow + hitting a pine tree just right, each branch sapping a bit of energy.
Comment: @Cadence As I said, nobody investigated so exactly what happened that night is unknown.  The snow itself wasn't enough to save him, especially as he was unconscious and thus took no steps to soften the landing.
Comment: This is gonna be harder than expected, Thanks!
Comment: A deep snowdrift should also work
Comment: If I recall properly. In the book "Angels and demons" a character survives a fall from a high altitude by  using a helicopter ¿door?. Basically used the square meter theory with a piece of debris from an exploding flying machine.
Answer: Can the character open a portal which points in arbitrary directions?
If falling, the character only has to open the portal so that the exit points upwards. Then then enter the portal, and come out going upwards. Gravity slows them down, and when they reach the highest point and start to descend again, they open a portal directly under them with the exit just above the ground, and they fall out and hit the ground going at a very reasonable speed. Timed correctly, they can probably land on their feet and walk off.
If they cannot point the portal in a new direction, so they always head downwards, taey should set the portal up with the exit directly above the entrance, with some very soft material in the middle to gradually bleed off speed.
For example, if you can locate a column of air which is rapidly rising, say above a large fan such as those skydiving trainer machines, then repeatedly falling from top to bottom through the air column would get you down to safe speeds.
Even repeatedly falling through trees, hay, snowdrifts, a kids ball pond, etc would work. If you can rapidly relocate the portal you could do this in a few inches of snow, just keep repositioning the portals so it seems like you have an infinitly deep snowbank.
Comment: Yea the character can place them anyway he wants so this could work, Thanks alot!
Answer: The human body can be very robust and there are known situations where people have survived free falls. In any scenario, what you want to do is reduce the impact, or better yet, the rate of deceleration your body will experience when it hits the ground and inevitably stops moving.
So here are a bunch of things that you could do
Landing Environment
There is a huge difference between landing on concrete, water, and a hay bale. The softer and voluminous the material, the better chance it has of decelerating you over a longer period of time and hence ensuring you survive the landing. Mythbusters has actually run a test that hitting water at high speeds would be like hitting concrete. Luckily, hitting water is better... but still a very risky business. So if your human can aim for something soft, something that will break or injur him but not kill him outright, they will have a better change (e.g. Going through a tin roof into a hay bale could save them, because the tin roof absorbs some of the impact, and the hay absorbs a bit more. Your human is still however seriously injured).
In addition to this, landing on angled ground is a huge factor in surviving a fall. This way you can redirect some of your speed into a sideways motion instead of straight into the ground with no where to go. Landing on a slope or positioning yourself so you are moving horizontally can be a great way to disperse the impact force.
Landing Posture
Landing posture is also an important part. Landing head first is a sure fire way to make sure you never survive. Landing on your legs however will ensure that your legs break first, dispersing some of that energy and giving you more time to decelerate as your body collapses on itself. Ideally you want to use your entire body as one huge spring to help redirect that energy and provide yourself more time to slow down. The aim would be to land on your heels (we are trying to come in at an angle here), bend your knees and assume a rolling motion like you see in those parkour videos. I'm at bit dubious as to weather you would be able to move fast enough (its just on the edge of believable) or if you would just snap your legs like twigs.
Falling Posture
Moving onto the actual part where you are in the air. Your posture is going to be huge in determining your terminal velocity. Spread yourself out to catch as much of the air as you can to slow yourself down. You however don't want to spin out or lose control, otherwise you might have trouble performing positioning  yourself or steering yourself towards a suitable landing spot.
Makeshift Parachute
The final thing left in your control is having a makeshift parachute. Similar to how a sugarglider uses its skin folds to help glide, you want to use anything you can get your hands on to help act as a parachute and decelerate you. A giant piece of card board (Again performed on Mythbusters) could easily be life saving. Outside of that, using your clothes, opening those buttoned T-shirts and taking your pants off to drag in the wind could all help slow you down just enough to survive.
Comment: of all the survivors from high height, none survived after hitting water. And there is no difference in hitting water or concrete when you are traveling at terminal velocity.
Comment: Hitting water is not a good idea. Taking for granted that one will lose consciousness as consequence of the fall, being unconscious in water is a sure recipe for feeding the fishes.
Comment: @L.Dutch Hitting water however is still a better idea than hitting concrete.
Comment: Thanks so much I'll have to think about this stuff!
Comment: @L.Dutch I read about a Navy pilot who's plane crashed after something went wrong with a refueling. His parachute failed to deploy, and he fell into the ocean and blacked out. He woke up shortly later and barely managed to get into the flotation device. After some intensive medical work and therapy, he was able to fly again.
Answer: The power he has to create portals also lets him create an energy field around his body that acts like a full-body airbag, causing the deceleration to begin slightly before he impacts a surface, decreasing the deceleration to a survivable level.
Alternatively, his power might simply make him momentarily invulnerable during decelerations once he reaches a certain speed, so that when he hits the ground, he doesn't break- the ground does, and he walks out of the resulting crater unharmed.
Comment: I might run with that, thank you very much!!
Answer: As FlyingLemmingSoup mentioned above, stretching out the time for falling is probably the best way to go if you can't reverse the direction of the portal.
Artificial cushion
One solution relies on clear-headedness while falling, really good timing, and the ability to rapidly make new portals.
If you're in an area without anything to cushion your fall, use portals to turn the ground into a makeshift cushion. Start by getting into a good landing posture, wait until just after your feet hit the ground and you've slowed slightly, but haven't injured yourself yet (this is where timing is important), then open a portal directly below you that leads to your right and about a foot up. Repeat this process, bleeding off a little bit of speed every time, until you come to a safe stop.
If you want it to look cool(er), but take more concentration, reduce the vertical distance that the portal moves, and horizontally move back and forth between the same few location. It will look a little "glitchy" from the outside, but you'll effectively slow yourself.
Artificial Ladders
A variation of the above that relies more on personal strength/agility, rather than portal-making ability, is to place a portal on the ground and another one slightly above it, with no need to move them until you've stopped. This requires the portal edges to not be sharp. You'll also want to be wearing gloves.
When you pass through the ground portal, use your hands to lightly "push" against the ground on either edge of the portal, then immediately retract them (don't want to break your arms/wrists/fingers). Repeat this on every pass through the portal. As long as you exert more force on the ground than the additional speed you gain from falling you'll eventually stop. This is effectively like falling between two infinite ladders, using the rungs to slow your fall. Gloves are very important here (especially if the ground is rough) as the friction and force will do a number on the skin of your hands otherwise.


Statistics interview questions

Question: I am looking for some statistics (and probability, I guess) interview questions, from the most basic through the more advanced. Answers are not necessary (although links to specific questions on this site would do well).
Comment: One example: http://stats.stackexchange.com/questions/4768/amoeba-interview-question
Comment: It would be very interesting if somebody could give examples they where given themselves when interviewed ...
Answer: Not sure what the job is, but I think "Explain x to a novice" would probably be good-
a) because they will probably need to do this in the job
b) it's a good test of understanding, I reckon.
Comment: (+1): I cannot count the times I thought I've understood something, but then I failed to explain it to someone else in easy words. Example: p-value ;)
Comment: "If you can't explain it to a six-year-old, then you probably don't understand it yourself" - Albert Einstein. Maybe not that extreme, but you get the point... :)
Comment: I like "Explain a p-value", with or without the "to a novice" part.
Comment: Really good advice whether you're interviewing or not!
Comment: this is why cross-validated is great. lots of "layman" questions and answers.
Answer: Standard Q where I work is along the lines of:

Have a look at this output of a multiple logistic regression from a statistical package you claim to have used (preferably one we use too). XXX is the independent variable of principal interest. How woud you interpret the results for a colleague with knowledge of the subject matter but no formal statistical training? (If necessary prompt for separate interpretation of point estimate, CI, p-value).
Comment: In more academic contexts one may also ask: 'have a look at this model output in this paper *that you (co-)authored*.  Tell me what it means.'  Underwhelming answers are then fatal because there are no unfamiliarity excuses available, yet dismayingly common.
Comment: @conjugateprior Not true. So long as there is at least one co-author who is not present, it was the not present co-author's area.  The main use of this technique is at conference presentations.
Answer: You might also want to reflect on whether the interview is the best medium for measuring the construct of interest.
If you want to measure prior knowledge of probability or statistics, you might be better off relying more on a written test.
You can ask more questions, and thus increase reliability of measurement. It's more standardised both in administration, and in scoring. And once the instrument is developed, it probably uses fewer resources to administer.
You could then use the interview as a more focussed tool looking at factors such as verbal and interpersonal skills.
Comment: This is a good point. I have found in the past that it is very difficult to tell whether a given candidate will work out, unless you have worked with them in the past.
Answer: Many questions/answers on this site could give ideas for good questions.  I will give a list with some such links that I think are good. Posts where I answered are overrepresented, because I know those posts better, not because they necessarily are the best!  I give short comments to each link, so you can decide if you want to follow the link.
What is the intuition behind SVD?    "Can you explain to one of our clients how the SVD works?"
Maximum Likelihood Estimation (MLE) in layman terms   "Can you explain in nontechnical language the idea of maximum likelihood estimation?"
Taleb and the Black Swan     "Tell me, what is a black swan, and why is that relevant? When is it relevant?"
Statistical inference when the sample "is" the population   "What can you say about statistical inference when the sample is the whole population?"
Goodness of fit and which model to choose linear regression or Poisson     "We have a regression problem where the response is a count variable.  Which would you choose in this context,  ordinary least squares or Poisson regression (or maybe some other)? Explain your choice, what is the main differences between these models?"
What is the difference between finite and infinite variance    "Can you explain, in as simple a language as is possible, what it means for a random variable to have infinite expectation or infinite variance?  What is the practical importance of this distinction?  Explain with an example."
What are modern, easily used alternatives to stepwise regression?    "How would you build a complex regression model when there are many possible predictor variables?  Describe different possible strategies, and tell about the problems with each of them"
How to deal with perfect separation in logistic regression?     "What is the problem of separation in logistic regression, its causes, symptoms? What can you do to solve it, if it is really a problem?"
Why does correlation matrix need to be positive semi-definite and what does it mean to be or not to be positive semi-definite?          and
What does a non positive definite covariance matrix tell me about my data?   "Explain why a covariance matrix must be positive (semi) definite, and what that means.  How can that fact be used?"
What are the multidimensional versions of median     "Can you propose some way to generalize the median to multivariate data?"
Interpreting interaction terms in logit regression with categorical variables      and     What are best practices in identifying interaction effects?      and       Two negative main effects yet positive interaction effect?       and       Including the interaction but not the main effects in a model       and       How to interpret main effects when the interaction effect is not significant?     "Explain what is meant by interaction in regression models.  Specifically, what does it mean if interaction is significant while main effects are not?  Is there some difference in interpretation of interaction between ordinary linear regression and logistic regression?"
What could be the reason for using square root transformation on data?  and  Appropriate data transformation    "When, how and why do you transform the response variable in a regression (or ANOVA) model?  Are there any alternatives?
Can I trust ANOVA results for a non-normally distributed DV?    "How would you treat an ANOVA with non-normal residuals?
Why is statistics useful when many things that matter are one shot things?
How can I efficiently model the sum of Bernoulli random variables?
When to use generalized estimating equations vs. mixed effects models?
What is happening here, when I use squared loss in logistic regression setting? "Why do we use maximum likelihood for logistic regression? Why not least squares?"
What is the difference between linear regression on y with x and x with y?
Answer: Two questions I've been asked:
1)  You fit a multiple regression to examine the effect of a particular variable a worker in another department is interested in.  The variable comes back insignificant, but your co-worker says that this is impossible as it is known to have an effect.  What would you say/do?
2)  You have 1000 variables and 100 observations.  You would like to find the significant variables for a particular response.  What would you do?
Comment: There are many reasonable responses to both, here are my quick thoughts: 1) the regression model is from a sample, this sample has random variation and therefore the model is only an estimate and can result in type 1 or type 2 errors.  There could also be heavy collinearity among the predictors.  For 2) it's the big P vs small N problem.  There are many techniques to handle this situation, such as reducing the dimensions and Lasso.
Comment: Could you post the answers as well?
For 1) I assume, there might be some dependent variables causing the problem. For 2) I would probably go for χ² (chi-squared) statistic test
Comment: 2) do univariate fits of variables and identify the ones which are most significant to reduce the variable set
Comment: 1) It may be a very low powered test (small N).  Run power analysis/suggest larger sample is needed.
Answer:
Here is a big data set. What is your
  plan for dealing with outliers? How
  about missing values? How about transformations?

Can they deal with real-world data?
Comment: Dear anonymous user, please don't use edit for comments (it is not for you, Neil).
Answer: I was asked once how I would explain the relevance of the central limit theorem to a class of freshmen in the social sciences that barely have knowledge about statistics.
Comment: The relevance of the Central Limit Theorem is is to make people think everything is Normal, when in fact nothing is. And therefore leads to many erroneous conclusions.
Answer:
How do you prevent over-fitting when
  you are creating a statistical model?

Good answer: cross-validation
Answer:
How do you numericize something that
is not numerical?

Example, "Automatic Feature Extraction for Classifying Audio Data"
Rationale: Can they figure out how to analyze something statistically that is not already in a big table?
Comment: @Iamanon https://link.springer.com/content/pdf/10.1007/s10994-005-5824-7.pdf
Answer: I often ask "how would you define/explain what forecasting is?"
Answer to that type of very general question helps me to see if people are connected to a particular case of forecasting. There is not a right answer but answering this synthetically during an interview is not always easy:)
Answer: For an observational data context:
Consider this regression model applied to this substantive problem.  What, if anything, in it can be interpreted causally?  [Further probe] What would you need to learn to change your opinion?
Answer: How will you count the number of sandal wood trees in Bangalore ?
Comment: Good question. I've used a version of this in class (trees in a park). They get the idea of sampling, but tend to miss the need for operational definition: when do you start calling it a tree?
Comment: Is that meant as a kind of [Fermi question](http://en.wikipedia.org/wiki/Fermi_problem)?
Answer: Under the heading Causation vs correlation:
It's common to use customer/user engagement as features for a predictive model. For example, people who click on this button at more likely to subscribe than people who don't. People who shop on Mondays are more likely to shop again than those who shop on Tuesdays.
If we take this to an extreme: Users who click "purchase" are more likely to purchase a product than users who don't click purchase.
But obviously that's not very helpful in explaining why some users subscribe and some do not.
How would you go about balancing using customer features which explain why they subscribe vs. those that are highly correlated with subscription, but are necessary to accomplish the task?
Answer: A lot of the questions we ask are similar to those that have already been described. But some that I haven't read yet, that are used: you might be asked to sketch out a program on a whiteboard to do something like: simulate a dice rolling or other probability problem, or calculate  a series of prime numbers (e.g. all the prime numbers that are less than 1,000,000) - you'd be able to do this in whatever language you wanted, but most people choose R, and some choose Python (I believe), but I guess you could choose Stata, SAS, SPSS, Matlab, etc. You'd probably be asked questions to probe the depth of your knowledge of your programming language of choice - why use apply instead of a for loop in R, for example.
You also might be asked to design an experiment or other study to investigate something - usually something practical - sometimes this will be related to the work that we do, but often not. (You're not supposed to have knowledge of the work that we do, but you should be able to grasp the gist of a problem you haven't heard of and speculate on it intelligently, even if given certain domain knowledge you'd know that was wrong - that's OK, you're not expected to have domain knowledge). You might be asked to take things like power into account.
Answer:
Here is a TinkerToy set. Show me
  how Euclidean distance works in three
  dimensions. Now show me how multiple regression works.

Can they explain how statistics works in the physical world?
Comment: if you want to scatter plot two variables with 100 observations, you only need 2 dimensions, not 100 :), and so on
Comment: Doesn't multiple regression with $N$ observations require an $N$-dimensional TinkerToy set though?
Answer: We are running a customer service centre. We are getting 1 million calls per month. How do we reduce it to ten thousand ?
Comment: This question is about 80–20 rule. It is a common rule of thumb in business; e.g., "80% of your sales come from 20% of your clients".  Microsoft noted that by fixing the top 20% most reported bugs, 80% of the errors and crashes would be eliminated. So it would mean set up an FAQ to identify address these 20% of the problems
Comment: remove 99% of your phones!
Comment: Stop paying the phone bill.
Comment: Incur a fee for the call.  (a 900-number in the US...)
Answer: While doing the variance analysis of quantitative variable, sometimes it found that frequency of the variable are very high (>5) then we use the Fisher's exact test to find independence of the variable.
Comment: Does the correct answer to this one include knowing that there is a controversy about whether fixed marginals make sense and having an informed opinion on the subject?
Comment: This would probably be subsumed under Chris's answer.
Answer: The average paid attendance at Yankees games last year was 55,000.  You randomly ask a bunch of people in NYC if they went to a Yankees game last season, and if they did, you record the paid attendance.  What is the average paid attendance for the games that the people you asked who went to a game attended?
I'll give you hint for my answer (hint was not provided): length-biased sampling.  I scored a home run on that, but it wasn't enough to win the game, ha ha.  Note: I mentioned many caveats pertaining to how the sampling was done, and the interviewer told me to disregard all of them.

Statistics interview questions


Alternative to arrowroot

Question: I have a lovely recipe (for stir-fried tofu) that uses arrowroot as its thickener. This is easy to use, and adds a nice subtle flavour of its own to the dish. However, I am now living somewhere where I can't find any - what would you recommend as an alternative? The flavours of the dish are quite delicate, and it is fried at a quite high heat.
Comment: Your profile says you are in Germany. Just yesterday, I stumbled over a product by Rintaura marketed as a sauce thickening product (don't remember the name exactly, something like Fix-binder) which appears to consist of 100% organic arrowroot starch. Bigger supermarkets often carry Rinatura products, I found this in a Kaufland.
Comment: You mention that it's fried at a high heat -- is it safe to assume that the tofu is coated in arrowroot, fried, then finished in the sauce?
Comment: No, the tofu is marinaded and fried, and the arrowroot is in the sauce, which is then added to the wok and fried until it thickens (half a minute or so).
Comment: @rumtscho - thanks, that's perfect! And I like that arrowroot is evidently called Pfeilwurzel (literally: "arrow root") :)
Answer: Corn starch (aka cornflour) will usually work and is more readily available, but it won't work well for acidic sauces, where you'll want to use tapioca starch.  (aka. cassava flour; if all you can find is tapioca in granule form, grind it up first).
For a more thorough list of starch based thickeners and their alternatives, see Cook's Thesaurus: Thickeners
Comment: Yup, +1 for tapioca, far better than corn or potato starch for recipes that ask for arrowroot.  If they already specify arrowroot, they probably do so for a reason (otherwise they'd just ask for corn starch!)
Comment: Thanks, that sounds like a great tip. I'll try it out :)
Answer: you should be able to use potato starch (or corn starch) as an alternative thickener.  Although  these will cause the sauce to become cloudy, rather than the clear of arrowroot.

Alternative to arrowroot


Do Professional and Semi professional cameras have "steadyshot" technology?

Question: Do professional and semi professional cameras have good optical image  stabilization, sometimes called steady shot?
Comment: SteadyShot is the Sony trademarked IS.  Not to be confused with SteadyCam, which is a physical stabilisation technology used in video.
Comment: High end Nikon lenses have what they call *vibration reduction* capability.  These lenses have VR in their full model designation.
Comment: And in the Canon world, the same tech is called "IS" for Internal Stabilization. Tamron calls it something else again, as does Sigma. It's all the same thing under the hood though.
Answer: In the DSLR world, different brands handle this differently.
Nikon, Canon and Panasonic camera bodies do not have any stabilization, rather some of their compatible lenses do implement image stabilization (the hardware is in the lens.)
Other brands, like Sony, Olympus, and Pentax, implement vibration reduction in the camera body, so that any lens used is stabilized.  The Sony version is called "SteadyShot".
Comment: It's worth mentioning that this is not just in the higher-end cameras and lenses — many entry-level cameras and lenses have this feature as well.
Comment: To further what mattdm stated, I think EVERY entry-level DSLR comes with an image stabilized zoom lens, and these days, the IS on those lenses is usually rated to about 3 stops of hand-holdability. It usually the 18-55mm kit lens, which is almost ubiquitous on entry-level DSLR's, and most other mid and pro-grade bodies also include an IS lens. Include sensor-level stabilization, I would say that makes IS a de-facto industry standard feature.
Answer: Most digital SLRs and many mirrorless interchangeable lens cameras — and many point and shoots — have optical image stabilization of some sort. But they all call it something different, and the technology used differs.
Olympus, Pentax, and Sony use a sensor-shift image stabilization approach very similar to that used for SteadyShot in Sony's camcorders. Sony even uses the same term. Exact details of implementation vary — for example, Pentax's system corrects for rotational shake, which is common when pressing the shutter release. You can read more about each of of these systems at each manufacturer's web site:

Sony SteadyShot Inside (SSI, or sometimes SSS, for "Super SteadyShot")
Pentax Shake Reduction (SR; note that's a pdf link)
Olympus Image Stabilizer (IS)

Canon, Nikon, and Panasonic take a different approach, providing many (but not all) lenses with elements which move to counteract shake. Again, there are differences in exact implementation (including types of movement which can be compensated for). More information at:

Canon Image Stabilization (IS or Hybrid IS)
Nikon Vibration Reduction (usually, just VR)
Panasonic Mega Optical Image Stabilization (Mega OIS, and I can't find a good link.)

Third-party lens makers also make lenses with this feature:

Sigma Optical Stabilizer (OS)
Tamron Vibration Compensation (VC)

The differences (including advantages and disadvantages) of these two approaches are well-covered here: What is the difference between in-lens image stabilizing and sensor-based image stabilizing?
Answer: If by "professional and semi professional cameras" you mean something like top and mid level DSLRs, the simple answer for Canon and Nikon is simply NO. The camera bodies have no built-in stabilization. Instead, optical stabilization, if present, is built into the lens, which is of course replaceable. Not all lenses have stabilization either.
Other brands like Sony or Pentax may have stabilization built into the camera body. Canon and Nikon are the most usual DSLR brands to see in professional hands though, by a wide margin.


How can I best describe "making a new discovery"?

Question: The context I am referring to is when someone, for instance,  comes into contact with something, a subject ( mathematics,  archeology or computer science, just to name a few),  a religion or a sport, and  discovers that he/she has found a new passion, something he/she  didn't know before or didn't think it could  be so fascinating. Is there an expression or an idiom to describe this ?
Answer: True calling

discovers that he/she has found a new passion, something he/she didn't know before or didn't think it could be so fascinating.

You could say that he/she has found his/her true calling. It means that this person has a divine gift/talent for said passion/profession.
Sources have defined it as: the activity by which one regularly makes a living (which I think isn't doing it justice), and a great etymology of how the term came to be used can be found here.

Example of how it can be used:
Person 1: Hey, did you hear about Roy? He's started painting, really seems to enjoy it and is quite passionate about it.
Person 2: Yeah, I guess you could say he's found his true calling.
Answer: Such a person could be described as having an epiphany (from the ancient Greek ἐπιφάνεια, epiphaneia, "manifestation, striking appearance" [thanks, Wikipedia]) or a revelation. They could also be said to have become infatuated with their new avocation or object of enthusiasm.
If you are specifically required to produce an idiom, consider also be consumed {heart and soul / body and soul}.
Comment: I thought of epiphany too but he requested an idiom or expression.  Hence, 'head over heels' or when one is [limerant][1] for the first time

  [1]: https://en.wikipedia.org/wiki/Limerence
Answer: You could describe the event of discovering something as:

the eureka moment
Definition: (idiomatic) The moment of a sudden unexpected discovery.

The first eureka moment
Answer: The idiom "light-bulb moment" would work well in this context.
Answer: Discovery is a generally accidental event that occurs when one's mined is preoccupied with some subject. For example, I made a significant discovery in discrete mathematics while sitting in a class discussion on basic tree theory. This led to over a year of research and is culminating in several papers to be published in mathematics journals.
To describe such a moment of self-discovery using something as short winded as an idiom may be sufficient, depending on how much of a role the moment plays in the individual's existence. If the individual is central to the telling of a story and the moment of discovery has an effect on the entire timeline, something more descriptive may be necessary:
"Something about that moment changed everything. Sammy couldn't get it out of her head. It kept her up at night, her mind feeding off of the intricacies and interplay of the universe that she suddenly felt she understood. Life was new, meaningful, and exciting. This could change the world, and nothing else mattered anymore."
Answer: I think a good word would be serendipity.

the fact of finding pleasant or useful things by chance

And one of my favorite quotes:

Innovation is serendipity, so you don't know what people will make.
Tim Berners-Lee
Answer: Consider "discover (or develop or grow) a passion for (something)."

He developed a passion for mathematics at the age of 12.
I've discovered a passion for archeology.
I first thought it would be in baseball, but then I grew an acute passion for the game of football.

Also, "take to" might work for what you're looking for.
take to: become fond of or attached to.

He took to mathematics at the age of 12.
I just took to archeology.


Why didn't Hannibal attack Rome after the Battle of Cannae?

Question: Hannibal Barca defeated 8 Roman legions in the Battle of Cannae. At that time Carthage also had control over Hispania. Why did Hannibal not seize Rome at that time?
Comment: Welcome to History:SE. Could you edit your question to clarify what you've looked into already, complete with links and references, and context if applicable? In particular, please let us know what you find missing or unclear about the Wikipedia entry on the topic, if one exists. This allows those who might want to answer to do so without needing to redo the work you've already done. You might find it helpful to review the site tour and Help Centre and, in particular, How to Ask.
Answer: Short Answer:

His army was too small to either assault or securely besiege Rome
Rome itself remain defended by two legions and a large, conscriptable population
Marching on and laying siege to Rome was beyond his logistical capacity
He cannot realistically defeat Rome while her Latin and Italian allies remained loyal

The traditional analysis is that Hannibal probably could not have taken Rome, and perhaps more importantly, knew that he couldn't, despite his brilliant victories in the field. A complementary analysis is that in recognition of this, his preferred strategy is to disrupt Rome's alliances.
Cities typically fall in one of three ways: being starved into submission, being taken by force, or outright surrendering. Rome was adamantly against peace, as evidenced by their rejection of Hannibal's terms (and probably, due to knowing their own strength). A successful siege was similarly unlikely; despite her devastating defeats, Rome remained very populous with plenty of manpower. While Roman allies in Italy remained loyal, Hannibal's army was too isolated and small to take on Rome on its own.
The prolific Punic Wars writer, Professor John Francis Lazenby from the Newcastle University, offers some convincing arguments about the difficulties Hannibal would have faced at Rome:

Lazeby advances several reasons why Hannibal did not march on Rome: Rome was 400 kilometres away, and there were two legions in the city to defend it, as well as the male members of the population; Rome still had troops and could raise others; whether Hannibal could take Rome quickly was uncertain and a siege could drag on; also Hannibal's aims were to detach the Latin and Italian allies from Rome. Hannibal did not want a war to the death with Rome; the war was about dignitas and imperium, and he proposed peace, though his ambassador to Rome, Carthalo, was turned back by the orders of Marcus Junius Pera, dictator for 216.
 - Dillon, Matthew, and Lynda Garland. Ancient Rome: A Sourcebook. Routledge, 2013.

This is AFAIK the predominant view. There are other viewpoints on why Hannibal couldn't take Rome, but I doubt many think that Hannibal had a moment of insanity and chose not to march on Rome for no good reason. For example, Professor John F. Shean argued that Hannibal was limited by logistics.

In any case it is unlikely that Hannibal could have realistically considered marching on Rome from Cannae. Shean convincingly argues that Hannibal's campaigns were largely dictated by his logistical situation, and that after Cannae his army scarcely had supplies for a few days, let alone a three-week march. If he had made it to Rome the subsequent siege could have lasted for months, if not years, posing a logistical nightmare since his army's opportunities for foraging would have been limited by being permanently stationed at one point. Even if Hannibal had wanted to follow up his victory at Cannae by marching on Rome, it is incredibly unlikely that he would have been able to do so.
 - Daly, Gregory. Cannae: The Experience of Battle in the Second Punic War. Psychology Press, 2003.
Comment: If Hannibal had tried to besiege Rome, he would have been trying to starve the Romans into surrender. This would have required his own army to remain stationary, effectively besieging himself. A small force in enemy territory has to stay mobile or be overwhelmed eventually, as Hannibal well knew.
Comment: Agreed - his goal wasn't to take Rome, but to detach the allies and remove its power to that of a local state.  He might have been able to do that, but failed.  Conquest was out of the question.
Comment: The other issue, critical in contemplating any siege, is whether Hannibal actually had a large enough force to meaningfully invest Rome. If he could not ensure keeping all Roman forces inside the city any attempt at siege was a very fast way to lose his own army, and thus the war, through self-starvation.
Answer: (Refer to map below)
After the Battle of Cannae (2 August 216 BC), Hannibal went immediately to Compsa (1), where he set up a base and took some of forces and sent them on a mission to collect allies in that area. He then gathered his main army and went to Naples (2) where he was hoping to take control of a seaport. When he got to Naples he found it had very strong walls and was determined to resist him, so he passed it by and went to Capua (3), a large city. At Capua the city agreed to ally with him and he occupied the city, although there were dissenters. He then turned south to reduce Nola (4), a smaller city. Nola submitted to Hannibal. However, the Roman Praetor Marcellus (blue dots) coming from Cassino caused Capua to swing back to Rome, then shadowed Hannibal to Nola. Hannibal then abandoned Nola and went first to the coast to see if he could get access to a port, but forces in Naples had become even stronger, so he went on to Nuceria (5), which he besieged and eventually captured by force, burning the city to the ground. Hannibal then returned to Nola (6), which Marcellus had occupied, and invested it, but Marcellus surprised him by sallying forth from the walls unexpectedly, killing a large number of Carthaginians, then retreating back within the walls of the city.

Having suffered this defeat Hannibal left off of Nola and went north to Acerra, which resisted him. He took the city, plundered it and then burned it. He then continued north to Capua and then to Cassino (7), a small town which was a Roman stronghold. He besieged this town, but could not take it (partially because the Volturnum River was part of the defenses), and winter was approaching so he retreated back into Capua where he made preparations to spend the winter.
Thus, Hannibal's campaign of 216 was over with him unable to even take Cassino, much less approach Rome.
So, you can see, Hannibal made every effort to advance onto Rome, but was unable to get past Cassino in 216, despite his success at Cannae.
Comment: Will you add the map?
Comment: @andy256 Can you not see the map?
Comment: No. If I go to edit mode, I see in the body where it *should* be, but in the normal view it is not visible to me.
Comment: PS I'm using Firefox 36.0.1
Comment: @andy256 Try that, it may because I had brackets in the text. Changed them to parentheses.
Comment: Sorry, still no map.
Comment: @andy256 The URL for the map is http://i.stack.imgur.com/E3vk3.jpg  can you access that URL?
Comment: Ah ha! It's waiting ... waiting ... and just stops with no error message. It's as though nothing (meaning something that is empty) is there.
Comment: @andy256 It's a pretty big image 1MB. I will try to make a smaller image. You can use i.stack.imgur.com/E3vk3m.jpg to get a medium sized image.
Comment: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/21830/discussion-between-andy256-and-tyler-durden).
Comment: @andy256 For some reason I can't log in to chat. I posted a new image.
Comment: Sorry, still nothing. I suggest deleting all our comments from yours down, and you post a request for others to indicate if they can see it or not. That would eliminate the possibility that the problem is local to me/my environment/Australia.
Comment: FWIW, I can see the map alright.
Answer: Hannibal's troops were not numerous enough (about 40,000 after the battle) to have a hope of taking Rome, which had a very large population (somewherere around 200,000) and was well fortified (the Servian Wall) and surrounded by allies who could launch surprise attacks against a besieging army.
The only real chance Hannibal had was turning those allies against Rome - which is exactly what he tried to do, for years, without decisive success.
Comment: But one could argue that Rome's army at the time was maybe even smaller, regarding Rome's population most of them would be slaves, possibly not so interested on who would rule them, Rome or Carthago
Comment: @JuanAntonioGomezMoriano I have learned a lot about Rome since writing this answer, and can respond now: first, slaves were not a majority of the population of rome, high estimates are 30%. Second, Roman slaves could hope to be freed, and in the case of a siege, that would be an obvious way to motivate them. They were unlikely to fare better in a sack of the city, as Carthago was also a slave-holding society.
Answer: Romans pulled on him the same trick the Greeks from Syracuse pulled on Carthage some 200 years prior when Carthage was laying siege to Syracuse. The Syracuse tyrant took almost all the men he could spare, sailed to Africa and rampaged around Carthaginian lands which forced the force near Syracuse to withdraw to face him, thus saving the city. Same thing, just Romans won the battle in Africa and Rome was never directly threatened (although Hannibal was "at the gates" he never attacked).
Simply, he did not have the manpower and resources to do so. He could only hope to turn all Latin people to his side and to gain a port so he could get reinforcements. It's amazing what he was able to do with such a little force deep inside enemy territory. Romans were also not sitting on their asses, but were constantly following him around, harassing and taking back cities he just left.
The thing that interests me more is why the Greeks didn't seize the chance and ally with Carthage to finish Rome off, seeing as Rome was a threat to all of them. Maybe they didn't take them seriously yet.
Comment: Sources would improve this answer, particularly since this contradicts my recollection of Roman history.  At least to my recollection, after Cannae, there were no Roman troops on Carthaginian soil.  My recollection is that nobody knows why Hannibal didn't follow up on his victory at Cannae. (Hat tip to @ed.hank for correcting my memory..
Answer: This is all speculation and since Carthage was literally wiped off the map eventually by Rome we can only draw inferences as we don't know what the strategic plans of Carthage were...if any. My educated guess is that Hannibal and his allies and Army had no intention of taking Rome without a follow on attack by a second Carthaginian Army or at least dramatic support from the "vaunted" Carthaginian Navy...neither of which Hannibal nor his Allies received.
His Army and Allies lived well in the Roman Countryside and Rome and her Allies certainly did not. But Rome then attacked North Africa not Hannibal's Army in Italy forcing him and ultimately all of his Army and Allies off the Italian Penninsula.
Answer: To answer the original question, let's set up a model of how the siege would have gone and compare it to a model of a field battle.
Pretend for a minute that Hannibal had a 10 man Army in the field against a comparable Roman Force.  That 10 man Army would be deployed in a contiguous formation with lateral lines of communication to all parts of the force (in other words, relatively simple to control).  Further more they would either be deployed to defend or oriented against a single piece of key terrain.  Most importantly, all 10 men are available to defend their key terrain or attack the key terrain against which they are oriented.  Hannibal was able to direct his full capability to such combat.  It's a 10 on 10 fight with Bill Belicheck coaching the Carthaginians and Greg Schiano coaching the Romans.
PRetend for a minute now that Hannibal has the same 10 men against the Romans inside Rome. Now the romans have a comparable trained military and 20 or 30 more peasants, blacksmiths, slaves, etc who can still swing a sword, hurl rocks, dump boiling oil, etc.  To assault these 30 or 40 pax inside their wall Hannibal now has to release 2 of his 10 to build and defend lines of contravallation (fortifications protecting his siege force), 2 of his 10 to scout for enemy reinforcements beyond the contravallation, 2 of his 10 to picket possible escape routes from the Roman wall, and 2 of his 10 build trenches, siege machines (if they are capable), and foraging.  Hannibal now has 2 men to assault the Romans 30 or 40 inside the wall.
Hannibal could dominate in the field because his Army was a field Army.  He was a maneuver specialist.  Siege warfare is not maneuver warfare.  He could nor more lead a successful siege against Rome then Hitler could mount an amphibious invasion of Britain.
Comment: Lots of opinion and irrelevant information, and no substantiation. Who are Bill Belicheck and Greg Schiano? What did they have to do with it? And what is the relevance of Hitler?
Answer: The answer to this question is very simple. He never thought of taking Rome, he always thought after Rome suffered so many defeats, the Battle of Cannae the worst,  he only thought that Rome will Sue for peace after so many defeats, many say the reasons why he didn't attack Rome was his army too small, or he was afraid of soldiers protecting Rome, what are you talking about? In every battle Hannibal's army was smaller in size than the Roman army and he still won because he was a genius and in every battle he had a surprise for Romans, the Battle of Lake(ambush) and the Battle of Cannae show that... So the answer is he could take Rome, but he didn't want too because he thought Rome would sue for peace.


Which visa should I apply for if I need at least two entries to the Schengen area?

Question: I hold an Indian passport and live in India.
I am planning to go to Croatia through France and then to Germany and go back to India through France again.
A double or mutiple entry Schengen Visa is required for Croatia.
Is it easier to get a Double entry Schengen visa than a multiple entry Schengen Visa for a first time tourist?
Comment: Do you plan to _enter_ France on the way to Croatia? (In fact, will you spend any time in France other than changing planes? If not you will be applying to Germany for the visa, not France.)
Comment: I will spend 2 days in France, 2 in Prague, 3 in Croatia, 4 in Italy, 2 in Germany and finally one in France again before the return flight. I didn't mention Italy earlier because the itinerary wasn't finalized. Now it is :)
Answer: Double-entry visas are created exactly for itineraries like the one you describe, and is probably what you will get issued when you apply.  You can always try checking the box for requesting multiple entries, but it's unlikely you will get that as a first-time traveler -- unless you have an extremely good story why you would need to make frequent and repeated visits to the Schengen area in the future.
(Be aware that since you're planning to spend the longest time in Italy, you must apply for the visa at the Italian consulate, even though you're entering and leaving through France).
Comment: I was planning the same. Thank you for the confirmation.


An argument that everything exists

Question: This is similar to my previous question, here: An argument that everything is possible. I have an argument that everything exists. For, that which does not exist is not a thing at all. For example, the term "unicorn", is merely a term. It is just a word that does not refer to anything. So, my question is, has any other philosopher made this argument? And is it a good argument?
Comment: I'd go so far as to say that this is not an argument at all, but simply a definition of the word "thing".
Comment: Isn't this just the [Ontological Argument](https://en.wikipedia.org/wiki/Ontological_argument)?
Comment: It sounds like a circular argument, i.e. something doesn't exist (e.g. a unicorn) because it doesn't exist.
Comment: Clearly that's not a good argument, if it's any argument at all. Who could doubt, that which does not exist is not a thing?

Sadly for your argument, the term "unicorn", is not an example. Does that not work for you?

Did you notice how "has any other philosopher made this argument…" implies that you are a philosopher?
Comment: For every truth there is approximately 2 million falsehoods. It depends on whether you think falsehoods are true.
Comment: Sounds something like Parmenides--the reconstruction of his argument [here](https://faculty.washington.edu/smcohen/320/parm1.htm) has his central thesis as "*That which is not* cannot be thought about or spoken about."
Comment: What about abstract things? Does justice exist? Does your own consciousness exist? If you answer the latter with "no, consciousness is not a thing," maybe this post will disappear in a puff of logic.
Comment: Concluding existence is not quite so easy. If I see something, that thing may exist in reality, or it may simply exist in my mind. All you can really conclude is that you exist, in some form or another. As Descartes famously said, ["I think, therefore I am"](https://en.wikipedia.org/wiki/Cogito,_ergo_sum).
Comment: Unicorns absolutely exist. But they are only ever fictional things, so they only ever exist fictionally.
Comment: Your argument is *short* of an antecedent of a sentence of a poem composed by an ancient saint "*If one thing is true, then everything is true...*"
Answer: You're apparently defining "thing" as "something that exists", which makes the statement "everything exists" a simple tautology and thus not very meaningful.
Comment: Not to mention that it immediately descends to "what is existence?"  In that sense it's the most essential philosophical question.

Unicorns exist, in imagination, in shared culture, even as an idea so powerful it gets applied to the most successful startups.

Isn't that an existence greater than a single grain of sand in the "real world "?
Answer:
I recommend distinguishing between object and word    (noun): on the one hand, objects exist; they are real. On the other hand,
some words refer to objects while other words do not. Hence all objects exist by definition, i.e. everything exists. That's not
philosophy, it's just correct language.

One may expand this consideration by introducing the term 'matter of
fact'. Then some words refer to 'matters of fact' while others do not; they refer to fictional relations.
Comment: Hmm, they're not written the same? More seriously, I use dictionaries. So, "thing" is the more general term. There doesn't seem to be any word more general than that. An object is something more specific: it is some thing towards which some action is directed.
Comment: @Speakpigeon, it depends on how you define "to exist" and "everything" (and these are not trivial by any means at all). Everything exists if the definition of "exist" means it's a physically observable object; and if "everything" means "physical objects". Or if you define "exist" as "we can think/reason about it" and "everything" as "all we can think/reason about". OP is playing a word-game, possibly without knowing. Changing any of the definitions (which would be perfectly acceptable as long as everyone involved knows which definition we are talking about) would possibly change the answer.
Comment: Numbers are not objects, but, presumably, you don't want to say they don't exist, right? And there is no reason to take "thing" as synonymous to "object".
Comment: @Speakpigeon How do you distinguish between the two terms 'object' and 'thing'?
Comment: @Speakpigeon "numbers are not objects": any entity that is not the subject is an object, either physical or metaphysical. The object is the counterpart of the subject. Subject observes, object is observed. Numbers are objects. Just like rocks or dark matter.
Comment: @RodolfoAP There are very different definitions, all well attested and all legitimate, so it all depends on which sense we use. Given that I was commenting on Jo Wehler's answer, I used the sense that an object is a tangible and visible entity. You use a sort relational sense. There is no debate. Numbers are objects in the sense you use and are not in the sense I used on this instance.
Comment: I don't think "everything exists" is a correct use of language at all. Firstly because in natural language "everything" does not have the same meaning as "every thing", and secondly because if we were to strictly obey the implied rule ("thou shalt not refer to anything nonexistent as an object or thing") then it would it very difficult to discuss fictional situations. It would forbid Arthur Conan Doyle to ever call Sherlock Holmes' pipe an object, for example.
Answer: Only if you're Humpty Dumpty

"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean—neither more nor less."

From Dictionary.com:-

a material object without life or consciousness;
an inanimate object.
some entity, object, or creature that is not or cannot be specifically designated or precisely described:
anything that is or may become an object of thought:
a fact, circumstance, or state of affairs:
an action, deed, event, or performance:

You have redefined the word "thing" to cover only the first 3 meanings.  You are specifically excluding meaning 4 which covers anything that can be imagined, whether it exists or not.
It is not a good argument, because it relies on you inventing a personal redefinition of a word in the English language, and furthermore that you are engaging in bad faith with anyone else when it comes to discussion because your personal redefinition is kept secret from them.  The purpose of language is to convey meaning.  Unless you preface any discussion with your new definition of the word "thing", then you cannot engage in rational discussion with anyone else.
And after that, you're back to the objections raised against your linked post.  If you redefine "thing" to mean "entities which physically exist", then "'that which does not exist is not a thing at all'" is a trivial restatement of your redefinition, not any kind of logical argument.
Answer: Depends on your definition of "exists" (obviously; the different definitions of "existence" for numbers  are well known) and the definition of "everything" which is not trivial at all (logical contradictions? non-constructive proofs of existence? only physical objects?).
Anyway, the closest argument to your question is probably the Level IV multiverse in Max Tegmark's book Our Mathematical Universe: My Quest for the Ultimate Nature of Reality. Short summary: if we accept that numbers (or generally, mathematical structures) exist, and the existence is independent on the raw substrate (the simulation argument), then our universe is not just described by, but is identical to a certain mathematical structure. By extension, any object described by a mathematical structure (i.e. by any reasonable, logically consistent description) exists. We can argue about the finer details, e.g. if we accept only computable or decidable or even finite structures, but that's about it.
Answer: I am unaware of any philosopher presenting this argument but IMO this argument is perceived in both ways - good one and bad one.
Allow me to elaborate with one small story -

In the time of the stone age, once there were two mothers talking. One was proud of her son because her son got selected for the hunting squad and she was telling the other mother of her son's gallantry and the other mother was complaining about her son saying that he spends his entire time in caves drawing paintings of their civilization.

The irony is, today we are able to figure out how people used to live in the stone age because of those paintings.
Coming back, today one of most useless tasks considered is teenagers posting useless videos on TikTok or YouTube. Now we all agree( and we should) that we don't know everything so there might be something good happening out of something stupid or bad also.
On other hand, sometimes I believe there is no meaning of creating new things or doing something. when we see something or do something new we help evolution process and pass our knowledge to future generation. And mind you, these are not depression thoughts or output of something negative but in all seriousness I believe sometimes there is no meaning. That Humankind shouldn't have evolved the way it have till now.
Think about it, let's say we learn more and more, and able to contact aliens then what next?
There is no way the population is going to decrease, scientist, innovators find ways to help humans and we have evil people blocking all this again. There is no way the evil is going to end. Even if we find ways to live on Mars, all these is going to continue on Mars also.
Comment: Ecclesiastes said much the same 3000 years ago.
Answer: I think a lot of answers miss that the question is actually interesting. It has been important in philosophy since its early beginnings.
Think about Plato's Sophist, which shows the argument between Parmenide's and Heraclite's schools, or Protagoras (as understood by Plato), through the voice of the Stranger from Elée. For Parmenide, what is is, and what is not is not. For Heraclite everything changes so nothing is ever what is it.
The answer Plato provides, accomplishing the so called parricide of Parmenide, is that even what is not is in a way. Something that could be called non-being, like nothing, something that is not in the world, something that is false, is already in a way, because we can think about it, talk about it, be influenced by it, believe it.
On the other hand, Plato doesn't flatten everything at all. An object that is in the world, is more, is really, compared to an object that is not. A speech that is true, is more than a speech that is false.
So he defends that middle ground, which is similar to what you say in a way, even if it is more complicated as you need to integrate all this with is ontological and cosmological system to really understand what he is saying.
Finally, this question is still discussed by contemporary fiction philosophers, as realists are saying : fiction characters exist, in a way, while others say that they don't exist.
You can also link this question to Aristotle's views on being, which is that being has multiple meanings, understood by many as a focal meaning of beeing : that which is is expressed in multiple fashion.
See https://orb.binghamton.edu/cgi/viewcontent.cgi?article=1192&context=sagp
I believe that answers that give a yes or no answer are missing the point that this question has been at the center of philosophical debates since thousands of years and is still ongoing. If you just say yes or no, followed by an argument, you are bringing something to the debate, but you miss the point that the debate is ongoing in a way.
Phenomenology, realism, analytic philosophy do not state the same thing about the answer.
Answer: Your argument is logically circular to the definition: if possibility is necessary for a thing to be, therefore things are only what is possible.
An equivalent --better and simpler-- argument would be "I am always right because you are wrong".

An argument that everything exists


Using Digital Still camera as webcam

Question: I have an old Sony DSC P-200 camera. Can I use it as a webcam. If so, how?
Comment: For which OS? connection or type of computer? any more details?
Comment: I got it working on Ubuntu for a Canon EOS camera, but it's not easy askubuntu.com/a/1110036/114641
Answer: My two cents are that for the amount of time and resources that you would have to put into accomplishing this, you could have bought a cheap little web cam.
Answer: Google says: Probably. You might start by watching Sony's video tutorial. Have you tried following a tutorial but run into problems?
Answer: Yes you can, but probably not as you think you can, so for how you probably WANT to do it the answer will be no.
You can use the camera as a generic video source connected to a video capture card.  You know... you can connect your camera to a TV to be able to watch the movies you record with it.  Well, if you purchase a video capture card for your computer, you can connect the Cybershot to the video capture card the same way.  Then, you can just start whatever video chat software you were planning on using (AIM, Yahoo, Skype, OoVoo, etc) and tell that software to use the Video Capture Card you installed.  Don't go looking for the software to find the Cybershot as the source... you are using the Video Capture Card as the source.
Now... if you were expecting or hoping to be able to just plug some USB cable directly between the camera and the computer... you can do that to dump pictures or video, but that's it.  You cannot use the camera as a webcam that way.  It just isn't made for that.
In short, if you want to spend some more money for the Video Capture Card, then you can do it... however, considering a USB Webcam will cost about as much as a Video Capture Card, you are better off just buying some Logitech QuickCam instead of trying to get your CyberShot to suffice.

Using Digital Still camera as webcam


Spider identification Delaware

Question: It looks like a wolf spider, but I've not seen these exact markings.
Comment: It could help if you gave indications of the size and environment.
Answer: That's a nice female Dolomedes tenebrosus - the upland Fishing Spider that lives in similar habitat to Wolf Spiders, and eats the same sort of foods.
The way it holds its long, stripey legs together (the front pair, anyway) is pretty standard for the Pisauridae, and the pattern on the body (while a bit variable in this species) is pretty distinctive.
https://bugguide.net/node/view/2011

Spider identification Delaware


Does Swami Vivekananda belong to Shankara parampara?

Question: Recently I listened to Swami Sarvapriyananda saying his "last name" is Puri, what about Swami Vivekananda? Does he belong to Adi Shankara parampara? And what about other modern swamis like Sivananda and Chinmayananda?
Comment: this is a duplicate question. Tota Puri gave sannyas to Ramakrishna. Ramakrishna gave sannyas to Vivekananda and the other direct monastic disciples. Hence, the Puri. All dasanami orders identify with one of the 4 major peethams. The connection between the different dasanami orders and the peethams has always been one of tradition, never one of actual direction.
Answer: The last name you are talking about is the name given to an advaitan monk in Daśanāmi Saṃpradāya.
The tradition gets its name because the followers of that tradition will be given ten names as suffixes after their Sannyasa name. The ten names are:

bhAratI,
sarasvatI
sAgara
tIrtha
purI
ASrama
giri
parvata
araNya and
vana.

These names are to be distributed among the four traditional Amnaya peethams established by Adi Shankaracharya. However, you will find it's nominal and sanyasis who have these names are not strictly affiliated to four peethams. It is traditionally said that Adi Shankaracharaya organized the Daśanāmi Saṃpradāya when he established four peethams in four directions.
Since, Ramakrishna Paramahamsa was initiated by a sanyasi named Totapuri, he also had a suffix puri. Even after Ramakrishna Paramahamsa, Vivekananda's disciples also got the suffix puri. Wikipedia lists many names of disciples of Ramakrishna and Vivekananda who have the suffix puri. Sivananda and Chinamaynanda have suffixes Sarasvati after their Sannyasa names.
According to Advaita-vedanta.org, (emphasis mine)

Modern Institutions: In addition to the more traditional advaita maThas and akhADas, various sannyAsIs of the daSanAmI order have established some of the more well-known modern institutions, like the Ramakrishna Math and Mission (swAmI vivekAnanda), the Self-Realization Fellowship (paramahamsa yogAnanda), the Divine Life Society (swAmI SivAnanda), Yoga Vedanta Center (swAmI vishNudevAnanda), the Chinmaya Mission (swAmI cinmayAnanda), and others. Among these, the founders of the Ramakrishna Mission, the Divine Life Society and the Chinmaya Mission trace their spiritual descent through the Sringeri paramparA. The Self-Realization Fellowship has links to the Puri paramparA.

Vivekananda and Chinmayananda do not belong strictly to Adi Shankara lineage but they trace their origin to the mathas established by him. They are from Daśanāmi Saṃpradāya.
Comment: I have only ever heard of four, tirtha, puri, sarasvati, and giri. Perhaps the others were once, but no longer or they are just subsets of the four mentioned. See also my comment in the question above.
Comment: @SwamiVishwananda Swami ji, there are still some sannyasis with the name Bharati in the country. I have heard of Kamalananda Bharati and Siddheshwarananda Bharati who are ekadandi sanyasis.
Comment: @swamivishwanand  swamiji bharati, saraswati, teerth samnyasi succession still exist in amnaya peethams. Others auch as puri doesn't exist in main line of shankaracharya any more. But others as mentiined above have those lines. Rest successions doesnt exist anymore. They were lost in time. This i heard from puri shankaracharya.
Answer: Sri Totapuri, a great Vedanti, was one of Sri Ramakrishna's gurus.  Probably that's where the sanyasis of Sri Ramakrishna Mission get their "Puri" title.  You can read more about Totapuri here:
https://www.ramakrishnavivekananda.info/gospel/introduction/totapuri.htm
Both Sri Ramakrishna and Swami Vivekananda used to talk about Sri Shankara often.  And some devotees of Swami Vivekananda think that Swamiji was a combination of Shankara's Jnana and Buddha's sacrifice.
However, I don't believe Swami Vivekananda belongs to Shankara parampara in the sense of lineage.


What happens internally when ESP8266 goes into deepsleep mode?

Question: What happens internally when ESP8266 goes to deep sleep mode. Is there any official documentation explaining that?
Answer: You can see this document https://www.losant.com/blog/making-the-esp8266-low-powered-with-deep-sleep
In summary, ESP8266 supports 3 sleep modes:

Modem-sleep
Light-sleep
Deep-sleep

Modem-sleep Mode
Modem-sleep mode is enabled only when ESP8266 connects to a router in station mode, via DTIM beacom mechanism. Within this mode, ESP8266 would wake up periodically, automatically, to handle arriving Beacon.
CPU and system are still on. Hence program that does not require constant network access could still run.
Light-sleep Mode
System clock is off and CPU is suspended. No program could run.
ESP8266 could be woken up via external GPIO level triggers.
Deep-sleep Mode
System clock and CPU are off.
ESP8266 could be woken up via
a) a low-level pulse generated on the EXT-RSTB pin via an external IO.
b) timer which is managed by the RTC
Answer: Have a look here as well, it is about clock gating and what actually happens when a micro goes to sleep. In short, to greatly reduce power consumption, internal peripherals (such as its ADC and so) are disabled.
Also, embedded.com has a neat explanation of what happens under the hood.


Looking for empty LEGO boxes for 6389 Fire Control Center and 6669 Diesel Daredevil

Question: I'm looking for empty LEGO boxes. I need two: one for 6389 Fire Control Center and one for 6669 Diesel Daredevil. Where could I find them?
Answer: You can buy boxes for most sets from Bricklink.com. For example, there are world-wide three sellers of the box for set 6389. Unfortunately, getting a box for such an old set will set you back $40-$50, excluding (international) shipping.
For set 6669 there are currently also 3 sellers, with prices ranging from $5 for a severely damaged box to $30 for boxes in good condition, all prices excl. shipping.
Of course there are other places to look, such as EBay or local classified sites like Craigslist in the US, but chances you find one of these boxes there are minimal. Bricklink (or its competitor BrickOwl) are your surest bet.


IOR in Blender Internal (raytraced)

Question: I'm confused about IOR in Blender Internal as used in raytraced transparency.
To demonstrate my issue, I set up a camera looking through a transparent sheet with IOR>1 (and slightly tinted) at a textured surface.
You can clearly see the expected refraction.
But when I flip normals, I get exactly the same render!
My question is therefore:  How does Blender Internal determine the "in/out"-side if it does not use the normals for that?
Placing the camera inside a properly closed transparent volume with IOR does not change anything.
Clearly, I can invert the IOR to treat camera rays, but I came across this issue when reflections going out and then back into the glass material misbehaved.
Comment: It doesn't use normals to determine where the ray is. It just swaps a traversal flag on ray pass.
Comment: I think this is the answer, result looks fine to me now, thank you!
Comment: @user2859 Feel free to add that as a proper answer
Answer: From user2859's comment:

It doesn't use normals to determine where the ray is. It just swaps a traversal flag on ray pass.

IOR in Blender Internal (raytraced)


Methods for propulsion other than rockets for leaving Earth's atmosphere?

Question: Due to the large amount of energy required, the standard method for leaving the Earth's atmosphere is rocket propulsion. Is there any other methods in development that don't involve rockets? E.g. solar sails, space elevators?
Answer: Currently existing, and for leaving the atmosphere? No. It's always a rocket engine of one kind of another, whether for vertical launch or horizontal, solid fuel or oxygen-hydrogen.
Developed - definitely yes.
Solar sail is only viable in space, considering solar wind it catches is a miniscule fraction of physical (air) wind force, meaning it would be torn to shreds in the upper atmosphere and never provide enough thrust to overcome earth gravity. Same for the ion engine which has minimal thrust nowhere near to overcoming earth gravity, but can produce that thrust for years at a time using up minimal amounts of energy and fuel.
But there is a number of planned methods of launch that wouldn't involve rocket engines. There are already a few groups working on the space elevator plans - we're quite far from it, because the only viable material - nanotubes - despite dirt cheap raw materials, are still prohibitively expensive to manufacture. There was a plan to use antarctic ice to build a launch tube similar to multi-stage cannon, to launch vehicles diagonally using land-bound explosive charges; that was stalled due to environmental concerns. There was a plan for a "partial space elevator" - a rope orbiting the Earth at LEO, with trailing end reachable by vehicles with air-breathing jet engines, docking their payload to it, then the payload lifted to the orbit and launching from the other end of the rope, using space propulsion (solar sail, ion drive) from there.
The problem with these all is that while operating them would be significantly cheaper than rocket engines - per-launch cost a fraction of current, their initial cost outweighs the cost of a rocket-powered vehicle many times over. With current economy, they are all on hold or proceeding at glacial pace with only minor, inexpensive side tasks completed, while the bulk of the work awaits funding.
Comment: Light beam propulsion was for "already in orbit" vehicles - a variant of the solar sail, where a stationary (orbital), large lens/mirror would focus sunlight on a small vehicle providing it with much more thrust than a solar sail alone could provide. Both the cannon and the railgun approaches have a problem of massive initial acceleration over very short time, likely lethal to any crew and damaging to precise equipment, they are considered viable for delivering raw materials for orbital manufacturing though.
Comment: @Paul: From what I recall, there were plans of ground-based mirror/laser array too, but they aren't very viable due to air dissipating most of the light over longer distances (and it would definitely not be able to lift any heavier crafts; light pressure is very weak and there's the problem that you can't remove absorption, give too much light over too small area and it burns a hole, increase surface and it gets heavy and vulnerable to wind.
Comment: Concerning space cannons, there is the "Thunder well" variant, blasting a payload to orbit with an underground nuclear detonation. It might have happened unintentionally during the plumbbob tests in 1957, less than two months before Sputnik. https://en.wikipedia.org/wiki/Operation_Plumbbob#Propulsion_of_steel_plate_cap However, I think it might be impractical and not even cheaper in theory...
Comment: I seem to recall that there was some research on using a light beam to push an object into orbit. Rail guns would be similar to the "multi-stage cannon" you mention.
Comment: The light beam research that I saw on TV was ground-based. If I recall correctly it used a pulsed beam to elevate a light-weight cone perhaps a few meters--very early research. I suspect such was not practical, but it also brings to mind the "possibility" of using a light beam to push the vehicle directly and expand a propellant--but that is probably *even less* practical.
Comment: The launch loop or space cable approach is pretty outlandish, but I think it would actually work. Aside from the outlandish initial cost to construct it, that is.
Comment: James Benford presented results this summer on experimental work on microwave-beamed sails, which can be used, theoretically, to take craft to orbit: http://www.youtube.com/watch?v=ef0aZ3zp1rk, starting at 28:56.
Comment: I'm not sure the "partial space elevator" would be dynamicaly stable. In a conventional space elevator, centripetal force keeps the rope tight. In this partial design, an object climbing the rope would pull down the top part.... Some form of active system would be needed to keep it in orbit.
Comment: @PhilMacKay: Of course as mentioned earlier: the "rope" needs to be actively adjusted for altitude loss caused by the "climbing" craft. Unlike classic elevator which could practically produce free energy, this one needs energy supply for each launch, just using it up more efficiently than chemical propulsion systems.
Answer: Multiple posters have mentioned but dismissed beanstalks because materials science isn't up to producing a sufficiently strong cable.  So far nobody has mentioned the other ladder into space approach--launch loops.  They don't require super materials because they are supported by objects moving faster than orbital velocity.  The big downside is that they are supported by moving objects--if they quit moving they fall.
The basic idea is you build two stations that will pitch iron bars back and forth.  You use extremely strong magnets to turn the bars around, once the bars are moving the energy input is minimal.  They originally fly back and forth on a ballistic trajectory.
Then you build a track on top of the flying bars.  The track deflects the bars downward, getting lift in the process.  The speed of the bars is upped to compensate--they continue to follow the same course.  Now you have what amounts to a train track that extends into space.  There's no upper limit on the speed of a maglev train in vacuum.
Technically possible:  Yes.
Cost:  Tremendous
Safety:  Not for me!

There's also the combination of the two ideas.
Build a set of towers in a ring around the Earth.  They support a tube, inside the tube you have an iron ring.  Spin the ring above orbital velocity, generate enough upward force to counteract the weight of the towers.  Since we have countered the load of the towers we are free to build higher.  Then build another ring to take the load.  Repeat until you are as high as you want to go.  If you're going past geosync the rings turn below orbital velocity in order to generate downward force rather than upward force.
Technically possible:  Yes.  You can build the rings and towers as close as needed to cope with material limits.
Cost:  Tremendous^2.
Safety:  While there are moving parts it's not like the launch loop that requires a turning station.

Answer: The key issue is, how do I accelerate this 'thing' to orbital velocity.
To date, only rockets have succeeded. Rockets are pretty efficient at generating high thrust with high impulse but are complex.
Other ideas touted in the part are thing like Orion, which used a giant vehicle, with a large plate, which on the downward facing side would detonate a nuclear device.  Then the plate would absorb the impact and connected via springs (huge as your would imagine) would transfer that momentum to the vehicle.  Clearly this is never going to happen. (Of course, the plot of the novell Footfall is that to repel an alien invasion, even Orion is acceptable). A rocket engine with no combustion, just riding the crest of nuclear explosions.
Other ideas are to use a high powered laser to heat a working fluid in the engine, so there is no rocket engine, combusting anything, rather the heated fluid exits the engine at high speed, transferring momentum.  A rocket engine, with no combustion really.
Orbital beanstalks, a cable from a base in GeoSync, dropping down to the surface of the Earth is an idea, and it is still science fiction for the most part.  (Cable needs to be 22,300 miles long.  Enough to wrap several times around the Earth.  It need a counterbalance weight or cable the same length sticking out the other way).  But this would be an approach to reaching orbit without a rocket.
Railguns, or high energy chemical guns are similar in approach, accelerate the vehicle in a gun.  Railguns work either by magnets (linear accelerator) or by vaporizing something with the current that generates the thrust.  Chemical guns light the fire behind the vehicle, but it is pushed by the edge of the explosion (Sort of confined, chemical Orion).
Alas, no anti-gravity or neat trick to get to orbit.
Comment: The acceleration gradient isn't symmetric about geosynch orbit, it's much steeper on earth side of geosynch. Without a counterweight, the cable would need to extend 144,000 km from earth's surface.
Comment: I would not say "never" about Orion. All it requires are different politics.
Answer: To get out of the atmosphere in any useful way, you have to accelerate to at least the velocity associated with a low Earth orbit, and do so without falling back to the ground before that velocity is achieved.
Ion drives will almost certainly never do this. They are much more efficient with propellant (much less propellant mass expended to achieve a given delta-V) than a chemical rocket, but cannot be built to deliver the necessary vehicle acceleration. You need at least 1g to balance surface gravity, and then some to get you moving up and away. Ion engines deliver very small fractions of a g; they work well for spacecraft already in space on long-term missions, but are not considered to ever be a space launch technology.
There are a couple of interesting technologies which could be applied to space launch.
One is the SABRE engine. If successful, it could replace vertical pad-launch rocket with runway take-off almost like a conventional airliner for access to orbit. Although effectively a rocket engine at high altitudes where there is insuffucient air to operate a jet engine, SABRE would operate as an air-breathing jet at lower altitudes, substantially reducing the mass of propellant the vehicle would require at lift of for flight to orbit, as compared to conventional rocket.
Another is the nuclear rocket. This was pioneerd in the 50s and 60s, pursued to the point where a feasible launch system could be built, although non ever was. The nuclear rocket replaces chemical reactions with nuclear reactions as the power source to produce a stream of hot gas for propulsion. The exhaust velocity would be much higher than that of any chemical rocket, significantly reducing the mass fraction of the vehicle's propellant.
Answer: JP Aerospace, which currently has the altitude record for airships at 95,085 feet, plans to fly airships to orbit. Once boyancy has taken it above almost all of the atmosphere, it will however use a rocket engine of sorts, an electrochemical propulsion which during several hours accelerates it to orbital velocity. Wikipedia has an overview of orbital airships and here's a lengthy radio interview with John Powell of JP Aerospace.
Answer: The critical issue isn't height but Speed. Could a combination of precooled jets, ion drives and rockets enable us to journey into space cheaper, safer and more efficiently than the current rocket based method? Using a precooled jet engine to gain altitude then using an ion drive to give extra thrust you could achieve the required velocity. Reversing the process you could land the craft conventionally removing the need for heat shields and other hefty re-entry devices. http://youtu.be/KFL623O9CXQ
Comment: No, Ion drives don't produce the needed thrust.  Until you have attained orbit time is of the essence and that rules out all low-thrust options.
Comment: The post repeats verbatim the 'Tube video's description. -1 for that and lack of verifiable calculations.


How to make Ubuntu backups readable on Windows

Question: I want to backup my files in Ubuntu 12.04 to an external drive in a way that they are accessible from my wife's computer which is not Ubuntu, it's Windows. How do I do that? I don't want any compression or encryption, just the files in their trees in a way that is readable when the external drive is connected to a Windows-based machine.
Answer:
The following is not suitable as a backup solution for Ubuntu

To save files for importing to a Windows OS the easiest would be to just format the external drive with FAT32 or NTFS and copy your files there. By this all files and their trees will be accessible from any Windows computer.
However with this method you will loose all Ubuntu file permissions. It is therefore not advisable to copy these files back to Ubuntu, it is more a one-way solution for sharing files from Ubuntu but not from Windowsb back to Ubuntu.
In case you need to keep your file permissions you will have to format your external drive with e.g. ext4, and install software on the Windows computer to read an Ubuntu file system:

How to read ext4 partitions in Windows?
Answer: The issue you have here is the filesystem you need to choose. The  systems where the different OS's are default happy with are not compatible, but there are ways around this.
The easiest is to format the disk in FAT32. This is a bit old, and you will have trouble with big files. There is a quite low upper-file-size limit of 4 Gb. So if you have DVD's, blu-ray or the like, you might get in trouble.
You can also use the windows-filesystem (NTFS) for linux. There used to be some trouble, but there is support for it now-adays. Choose this if you can't use FAT32
I would advice against choosing one of the 'default' systems from linux (EXT3, ReiserFS, etc) as their support in windows is limited to non-existend. WIth the above 2 options your wife will not have any problem reading the disk.