<div dir="ltr"><div>Hi Andrew,</div><div><br></div><div>I think the code is simply using the terms "variance" and "standard deviation" interchangeably here.</div><div><br></div><div>You can see how the `variance` array attached to the profile object is calculated here:</div><div><br></div><div><a href="https://bitbucket.org/yt_analysis/yt/src/09f0ef297d7068078a021fc8290d9e3519baf82d/yt/data_objects/profiles.py?at=yt&fileviewer=file-view-default#profiles.py-183">https://bitbucket.org/yt_analysis/yt/src/09f0ef297d7068078a021fc8290d9e3519baf82d/yt/data_objects/profiles.py?at=yt&fileviewer=file-view-default#profiles.py-183</a><br></div><div><br></div><div>I haven't looked up the mathematical definitions in detail, but I believe that this is the sample variance at each profile bin (*not* the standard deviation of the mean).</div><div><br></div><div>If you'd like, please feel free to send a pull request to update that cookbook recipe to label the variance with "variance" instead of "standard deviation". The code for the cookbook recipe is located here in the repository:</div><div><br></div><div><a href="https://bitbucket.org/yt_analysis/yt/src/09f0ef297d7068078a021fc8290d9e3519baf82d/doc/source/cookbook/profile_with_variance.py?at=yt&fileviewer=file-view-default">https://bitbucket.org/yt_analysis/yt/src/09f0ef297d7068078a021fc8290d9e3519baf82d/doc/source/cookbook/profile_with_variance.py?at=yt&fileviewer=file-view-default</a><br></div><div><br><div class="gmail_quote"><div>On Sun, Jan 1, 2017 at 8:30 AM Andrew Cunningham <<a href="mailto:ajcunn@gmail.com" target="_blank">ajcunn@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="gmail-m_1537963171831916159gmail_msg">In the following cookbook example:<br class="gmail-m_1537963171831916159gmail_msg"><div class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"><a href="http://yt-project.org/doc/cookbook/simple_plots.html#profiles-with-variance-values" class="gmail-m_1537963171831916159gmail_msg" target="_blank">http://yt-project.org/doc/<wbr>cookbook/simple_plots.html#<wbr>profiles-with-variance-values</a><br class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"></div><div class="gmail-m_1537963171831916159gmail_msg">the variance along the profile is extracted:<br class="gmail-m_1537963171831916159gmail_msg"><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg">variance</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">=</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">prof</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">.</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">variance</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">[</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-s gmail-m_1537963171831916159gmail_msg">'gas'</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">,</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-s gmail-m_1537963171831916159gmail_msg">'velocity_magnitude'</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">]</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">.</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">value<br class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"></span></div><div class="gmail-m_1537963171831916159gmail_msg"><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">but is then labelled as the standard deviation when the plot is created:</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg">plt</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">.</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">loglog</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">(</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">radius</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">,</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">variance</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">,</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">label</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">=</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-s gmail-m_1537963171831916159gmail_msg">'Standard Deviation'</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">)</span><br class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"></div><div class="gmail-m_1537963171831916159gmail_msg">So, does "prof.variance" return the standard deviation and not the variance?  Or, is the plot mislabelled?  Should the plot instead be:<br class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">plt</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">.</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">loglog</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">(</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">radius</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">,</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">np.sqrt(variance</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">),</span> <span class="gmail-m_1537963171831916159m_6290603254798811519gmail-n gmail-m_1537963171831916159gmail_msg">label</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-o gmail-m_1537963171831916159gmail_msg">=</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-s gmail-m_1537963171831916159gmail_msg">'Standard Deviation'</span><span class="gmail-m_1537963171831916159m_6290603254798811519gmail-p gmail-m_1537963171831916159gmail_msg">)</span><br class="gmail-m_1537963171831916159gmail_msg"><br class="gmail-m_1537963171831916159gmail_msg"></div></div><br><br>______________________________<wbr>_________________<br class="gmail-m_1537963171831916159gmail_msg"><br>yt-users mailing list<br class="gmail-m_1537963171831916159gmail_msg"><br><a href="mailto:yt-users@lists.spacepope.org" class="gmail-m_1537963171831916159gmail_msg" target="_blank">yt-users@lists.spacepope.org</a><br class="gmail-m_1537963171831916159gmail_msg"><br><a href="http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org" rel="noreferrer" class="gmail-m_1537963171831916159gmail_msg" target="_blank">http://lists.spacepope.org/<wbr>listinfo.cgi/yt-users-<wbr>spacepope.org</a><br class="gmail-m_1537963171831916159gmail_msg"><br></blockquote></div></div></div>