jk's profile - activity

I would probably do it like this:

C = -I*sqrt(pi)*x*e^(-1/4*x^2)
f=fast_callable(abs(C),vars=[x],domain=CC)
plot(f, (-10,10))

Thank You @Jason Grout. This methods works, but only if `domain=CC` is specified explicitly. Mind to explain?

@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.

I typically encounter expressions of the type

 C = -I*sqrt(pi)*x*e^(-1/4*x^2)
 Abs = abs(C)

Sage's built-in plot commands fails:

verbose 0 (4101: plot.py, generate_plot_points) WARNING: When plotting,
failed to evaluate function at 200 points.
verbose 0 (4101: plot.py, generate_plot_points) Last error message:
'unable to simplify to float approximation'

We can evaluate the expression numerically:

X = map(lambda x: x/10, range(-100,100))
Y = map(lambda xx: Abs.subs(x=xx).n(), X)
Yreal = map(real, Y)
Yimag = map(imag, Y)
list_plot(zip(X,Yreal)) + list_plot(zip(X,Yimag),color='red')

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.

The documentation has an example, which does exactly what you want:

• Sage Notebook server
• HTTPS
• No accounts for strangers

1. I want to run the Sage notebook server on a remote machine and be the only person allowed to log in. Type:

   notebook(interface='', secure=True)

First, I agree with @Xaver that some more end-user 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.

'unable to simplify to float approximation'

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

float(Pabrf)

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?