serious bug in _maxima_init_ method for formal derivatives with new symbolics

[williamstein]

sage: f(x) = function('f',x)
sage: g = f(-x).diff(x); g
-D[0](f)(-x)
sage: g._maxima_init_()
"(diff('f(x), x, 1))*(-1)"

Notice that the -x inside f is totally ignored! This is because of code in the derivative method around line 454 of sage/symbolic/expression_conversion.py

Changing the line

args = ex.args()

to

args = ex.operands()

"fixes" the problem, in that a NotImplementedError gets raised, instead of a wrong result returned. This is way better than the current situation, and we better fix this asap.

A better fix of course is to implement proper conversion. mhansen wrote this code, so maybe it would be easy for him.

CC: @golam-m-hossain @mwhansen

Component: calculus

Issue created by migration from https://trac.sagemath.org/ticket/6376

[burcin]

comment:2

Mike, do you have any time to look at this?

Thanks.

Burcin

[robert-marik]

comment:3

fixed with patch at #7401 which waits for review.

sage: f(x) = function('f',x)
sage: g = f(-x).diff(x); g
-D[0](f)(-x)
sage: g._maxima_init_()
"(at(diff('f(dummy_var_der), dummy_var_der,1),dummy_var_der=-x))*(-1)"

[robert-marik]

comment:4

The patch is attached to #7401

#6376 is not doctested, since I did not know about this issue when finished patch for #7401. It could be easily doctested, but doctests in #7401 are equivalent to #6376.

[kcrisman]

comment:5

Okay, this seems okay.

To release manager: please close this as fixed once #6376 is merged.