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20111020 12:12:19 +0100  marked best answer  Fast numerical plot command that always works? I would probably do it like this: 
20111020 12:12:07 +0100  commented answer  Fast numerical plot command that always works? Thank You @Jason Grout. This methods works, but only if `domain=CC` is specified explicitly. Mind to explain? 
20111018 19:44:36 +0100  commented question  Fast numerical plot command that always works? @Jason Grout, I update the question with an example and a link to a public worksheet. In this simple example, simplify() would solve the issue, but on more sophisticated expressions simplify will fail. 
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20111017 14:56:26 +0100  asked a question  Fast numerical plot command that always works? I typically encounter expressions of the type Sage's builtin plot commands fails: We can evaluate the expression numerically: This works, but looks like a dirty workaround. Should I use numpy arrays and fast_callable? Or use fast_callable() without numpy? Here is an example worksheet. 
20111017 14:43:11 +0100  answered a question  HTTPS for Sage Webserver? The documentation has an example, which does exactly what you want:

20111017 13:57:28 +0100  commented answer  Using symbolic expressions with numpy arrays First, I agree with @Xaver that some more enduser accessible documentation would be very helpful. Google only found [this](http://www.sagemath.org/doc/reference/sage/symbolic/expression_conversions.html), which does not appear to be a good starting point. Second, I'm not sure, whether this is the solution to OP's question. $f(x,y,z)$ is a function of three independent variables, so the general numeric result should be a $NxNxN$ matrix. 
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20110105 18:58:06 +0100  answered a question  Plotting question
Came here because I have a similar problem Apparently the plotting command provided by Sage evaluate expressions by coercing to float, i.e. plot calls
This fails on your expression because it's too complicated. Can someone explain why Sage doesn't evaluate expressions numerically when plotting? What would be a straightforward why to do this? 