Print the trace in the documentation

[remydutto]

In the 2D-example documentation, i cannot see the trace of the fsolve function while the showtrace is set to true.

[jbcaillau]

mr @ocots uses nothing # hide a lot 🤭

[ocots]

You should not merge while it is not working. The process:

• create an issue
• from the issue, create a branch
• you can make a PR (after a first commit which changes) but you should convert it as a draft while you are working on it
• when it is ok you can switch to "ready to review"

[ocots]

@remydutto Tu remarqueras un "Show trace now #6" qui correspond à la PR en cours car cette issue est liée à la PR #6.