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## #1660 'diff() inconsistent

closed
nobody
None
5
2009-11-29
2009-05-05
Žiga Lenarčič
No

'diff(x*y,x) gives the correct result (holds form), while
'diff(x,x) gives 1, calculates the differencial.

## Discussion

• I may be stupid or blind, but I do not see the problem here. Would you like to see diff(x*x,x) resulting in x rather than 2x? May be your remark is more subtle than this.

• Problem is in quoted diff, which should not evaluate, but it does in 'diff(x,x) case:
(%i2) 'diff(x*y,x);
d
(%o2) -- (x y)
dx
(%i3) 'diff(x,x);
(%o3) 1
(%i4) 'diff(2*x,x);
d
(%o4) -- (2 x)
dx

• Dieter Kaiser
2009-11-14

'diff(x,x) gives 1 because of simplification in the simplifying function simpderiv.

We have a similar simplification for integrals:

(%i9) 'integrate(1,x);
(%o9) x

Therefore, we can do something like

(%i10) 'diff('integrate(1,x),x);
(%o10) 1

Furthermore, the following simplification is build in:

(%i15) 'diff(x,x,0);
(%o15) x

This works for an arbitrary expression too:

(%i17) 'diff(sin(x),x,0);
(%o17) sin(x)

It might be arguable why Maxima does not do more simplifications of this type, but the implement simplifications are not wrong. I have no example, where these simplifications cause problems.

So, I would suggest not to change the behavior of Maxima to simplify the examples in this bug report.

Setting the status to pending and resolution "works for me".

Dieter Kaiser

• Dieter Kaiser
2009-11-14

• status: open --> pending

• This Tracker item was closed automatically by the system. It was
previously set to a Pending status, and the original submitter
did not respond within 14 days (the time period specified by