title: Plot negative values on a log scale
body: <p>I am doing some analysis to calculate the value of <code>log_10(x)</code> which is a negative number. I am now trying to plot these values, however, since the range of the answers is very large I would like to use a logarithmic scale for this. If I simply use <code>plt.yscale('log')</code> I get a message telling me <code>UserWarning: Data has no positive values, and therefore cannot be log-scaled.</code> I also cannot supply the values of <code>x</code> to <code>plt.plot</code> as the result of <code>log_10(x)</code> is so large and negative that the answer of <code>x**(log_10(x))</code> is simply <code>0</code>.</p>
  
  <p>What might be the most straightforward way of plotting this data?</p>