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    <p>It depends on the version of SymPy that you are using.</p> <p>In the latest version (0.7.2) you already have a plotting module that is guaranteed to be able to plot <em>anything</em> and that can use as a backend matplotlib.</p> <p>In older versions you have the option to use <code>lambdify</code> which is a hackish, mostly broken helper function that returns a fast numerical function to be used with numpy. However it breaks for non-trivial expressions.</p> <p>Below I explain how to use the plotting module in 0.7.2:</p> <ol> <li>Just call <code>plot</code> like in <code>p = plot(expression, (var, start, stop))</code>. If you have <code>matplotlib</code> it will use it directly.</li> <li>If you want something fancy, extract the <code>matplotlib</code> figure: <code>f = p._backend.fig</code>.</li> <li>Stop caring about SymPy, the rest of your work is in <code>matplotlib</code>. You can do whatever you want.</li> </ol> <p>The idea behind SymPy's plotting module is to be able to evaluate any possible expression, not to reimplement a plotting library like matplotlib. So just use <code>sympy.plotting.plot</code> for evaluation and do the fancy subplot transformations in matplotlib.</p> <p>Using the sympy plotting module has other advantages over hackish solutions: detection of discontinuities and adaptive sampling, coloring depending on a function, evaluation of pathologically complicated symbolic expressions (although slow).</p> <p>And obviously, check the docs. While they are not great, many questions are answered there: <a href="http://docs.sympy.org/0.7.2/modules/plotting.html">http://docs.sympy.org/0.7.2/modules/plotting.html</a> Check also the notebooks in the example folder of sympy.</p> <p>EDIT to address some additional questions:</p> <ol> <li><p>There is no notion of subplots in the SymPy's plotting module, and hopefully there will never be one. As I mentioned above, SymPy is not trying to reimplement modules like <code>matplotlib</code>, rather it is trying to give the tools necessary for good easy use within another module (interfaces between modules are better than big project with many small submodules).</p></li> <li><p>In order to create one figure with two subplots in matplotlib from two different sympy plots do (this is an ugly hack, as matplotlib does not support merges of figures):</p> <pre><code>sympy_p1 = sympy.plot(foo) sympy_p2 = sympy.plot(bar) matplotlib_fig = plt.figure() sp1 = matplotlib_fig.add_subplot(121) sp2 = matplotlib_fig.add_subplot(122) sp1.add_collection(sympy_p1._backend.ax.get_children()[appropriate_index]) sp2.add_collection(sympy_p2._backend.ax.get_children()[appropriate_index]) matplotlib_fig.show() </code></pre></li> <li><p>In order to update sympy plot (not creation of a subplot, just adding a new expression) use <code>sympy_p1.append(sympy_p2)</code>. This will result in <code>sympy_p1</code> containing the plots of both <code>foo</code> and <code>bar</code> (<strong>NOT</strong> two subplots, rather one plot with both expressions).</p></li> <li><p>You might want to use <code>sympy.plot(..., show=False)</code> in some cases.</p></li> </ol>
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    1. COThe thing I miss and also the docs don't say is how to cause sympy to reuse a figure rather than opening a new one. In your suggestion, how do I generate two plots using sympy in two different subplots of matplotlib? Thanks!
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    2. CO@UriCohen, I think I have answered your questions in the edit that I made above. I have not tested the code but it should work - if there is a problem just warn me and I will fix it.
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    3. COI think the latest version of sympy don't have _backend in the Plot object, just backend which is a DefaultBackend instance without an ax member...
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