Comment #10 on issue 2571 by renato.c...@gmail.com: Regression in
Integral.subs
http://code.google.com/p/sympy/issues/detail?id=2571
There's no sense putting the 5 inside the Integral
Sorry, what I meant here was: there's no sense in integrating wrt a number
(that's why I said it should raise), so when you use subs(x, 5) on an
Integral, you can only mean one of two things:
* evaluate the expression at x=5 (gives current result, Integral(x, (x, 5))
- I overlooked this form of expressing this, Subs is not needed)
* replace all occurrences of x in the integrand with 5.
As you noted, I tend to think of subs() as an "eval" function. In
particular, I expect that if mathematically a == b (f.e. if a.doit() == b),
then we should have a.subs(old, new) == b.subs(old, new) (mathematically).
I'm not sure if subs() currently satisfies this, but it may if old is a
Symbol.
The documentation of subs() doesn't clarify if the relation above should
hold or not, I think different people are using subs() with different
meanings in mind, which certainly confuses matters. In case we go
with "subs() replaces anywhere in the expression irrespective of
mathematical meaning", I think we should implement an alternative that does
keep the mathematical equality.
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