Option to hold for derivative

[vaibhavkarve]

It would be nice to have the output of

(x^3).diff(x, hold=True)

look like

$$ \frac{\partial}{\partial x}x^3 $$

Component: calculus

Keywords: hold

Author: Ralf Stephan

Branch/Commit: u/rws/option_to_hold_for_derivative @ 453cf14

Issue created by migration from https://trac.sagemath.org/ticket/24861

[rwst]

comment:1

Although we don't exactly have already a ticket for this, see the related #17445 and #15021.

[rwst]

Branch: u/rws/option_to_hold_for_derivative

[sagetrac-git]

Commit: 453cf14

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

453cf14

24861: handle multi diffs

[rwst]

Author: Ralf Stephan

[rwst]

comment:4

Thanks for the report. This will be a useful addition to Sage.

[bryangingechen]

comment:5

I agree this would be a nice addition; thanks for addressing this. Here are some comments.

In src/sage/functions/other.py:

• Something like (x).diff(x*x, hold=True) returns diff(x, x^2) instead of an error. Note also that latex((x).diff(x*x, hold=True)) causes a segfault.
• The error message wrong argument in diff could be made more helpful; perhaps something like all arguments to diff must be symbols or numerical values. This should be tested as well.
• The LaTeX output should include parentheses around the expression (probably with \left and \right), otherwise something like latex((x^3+y).diff(x,2,y,2, hold=True)) returns {\frac{\partial^{4}}{{\partial x^2}{\partial y^2}} x^{3} + y} which is incorrect.

In src/sage/symbolic/expression.pyx:

• the hold parameter should be added to the docstring of derivative. I also noticed a typo in the first line of the docstring as well: this expressions -> this expression.