Why does the result of my sage command becomes question mark? - tex

Question

I'm trying to use sagetex package, but then I found this kind of problem when running the code
the result
Here is the code I tried to run:
\documentclass{article}
\usepackage{sagetex}
\usepackage{graphicx}
\usepackage{fancyvrb}
\begin{document}
Using Sage\TeX, one can use Sage to compute things and put them into
your \LaTeX{} document. For example, there are
$\sage{number_of_partitions(1269)}$ integer partitions of $1269$.
You don't need to compute the number yourself, or even cut and paste
it from somewhere.
Here's some Sage code:
\begin{sageblock}
f(x) = exp(x) * sin(2*x)
\end{sageblock}
The second derivative of $f$ is
\[
\frac{\mathrm{d}^{2}}{\mathrm{d}x^{2}} \sage{f(x)} =
\sage{diff(f, x, 2)(x)}.
\]
Here's a plot of $f$ from $-1$ to $1$:
\sageplot{plot(f, -1, 1)}
\sageplot[scale=.5]{plot3d(sin(pi*(x^2+y^2))/2,(x,-1,1),(y,-1,1))}
we know that 2010 factors to $\sage{factor(2010)}$
\begin{sagesilent}
m=identity_matrix(QQ,3)
m[0]=m[0]+m[1]
m[1]=m[1]-m[2]
m[2]=m[2]-2*m[1]
m[1]=m[1]+3*m[0]
m[0]=2*m[0]
\end{sagesilent}
Compute the rref of $\sage{m}$
\begin{sageblock}
g(x)=taylor(tan(x),x,0,10)
\end{sageblock}
$$\tan(x)=\sage{g(x)}$$
\end{document}

Answer 1

When I try to compile this, I get:
**** Error in Sage code on line 23 of file.tex! Traceback follows.
Traceback (most recent call last):
File "file.sagetex.sage.py", line 39, in <module>
_st_.plot(_sage_const_1 , format='notprovided', _p_=plot3d(sin(pi*(x**_sage_const_2 +y**_sage_const_2 ))/_sage_const_2 ,(x,-_sage_const_1 ,_sage_const_1 ),(y,-_sage_const_1 ,_sage_const_1 )))
NameError: name 'y' is not defined
Once a single error occurs, the rest of the Sage output may be lost, leading to all of the question marks. The problem is this line:
\sageplot[scale=.5]{plot3d(sin(pi*(x^2+y^2))/2,(x,-1,1),(y,-1,1))}
and in particular, you have not defined y. (In SageMath, x is automatically defined to be a variable, but not y.) If you add this before the plot, it should work:
\begin{sagesilent}
var('y')
\end{sagesilent}