title: Plotting straight line on semilog plot with matplotlib
body: <p><img src="https://i.stack.imgur.com/8uIu4.png" alt="enter image description here"></p>
  
  <p>This isn't, strictly speaking, a semilogy plot.  I used this code to get a logarithmic <code>y-axis</code>:</p>
  
  <pre><code>pyplot.gca().set_yscale('log')
  </code></pre>
  
  <p>edit:  Okay maybe I'm dumbing it down too much.  I need to plot straight lines, from the x-axis at a 45 degree angle.  Similar to the line in the image, but actually straight and at a 45 degree angle.  I also need to shift any x-value based solely on its y-value.  </p>
  
  <p>What is the formula for plotting a straight line for known y-values and unknown x-values at a 45 degree angle?  (Perhaps a math forum would be more appropriate?)</p>
  
  <p>My education is at a pretty low level, so for instance I had to teach myself what logarithms are the other day because I had never learned in school.  So I'm not able to work out a way to plot straight lines on my own.  </p>