Updates:
Labels: WrongResult
Comment #1 on issue 3328 by [email protected]: Integrating simple
DiracDelta
http://code.google.com/p/sympy/issues/detail?id=3328
Another issues here: I can't get the G-function integral to not give
piecewise. The conds argument is ignored.
Interestingly, it seems the the complex piecewise expression reduces to
just Piecewise((0, z > 1), (-1, True)) for z in (0, oo). So the answer is
just -1.
And I guess this is wrong then:
In [80]: integrate(integrate(DiracDelta(-z + x - y), (z, 0, oo)), (x, 0, 1))
Out[80]:
⎧ │1│
-⎪ 0 for │─│ < 1
⎪ │y│
⎪
⎨ 1 for │y│ < 1
⎪
⎪ ╭─╮0, 2 ⎛2, 1 │ 1⎞
⎪y⋅│╶┐ ⎜ │ ─⎟ otherwise
⎩ ╰─╯2, 2 ⎝ 1, 0 │ y⎠
In [81]: integrate(integrate(integrate(DiracDelta(-z + x - y), (z, 0, oo)),
(x, 0, 1)), (y, 0, 1))
Out[81]: 0
The answer is clearly -1 (on y = 0..1, |y| < 1, so the integrand is just
-1).
Also, the printing is not correct there, but I'll open a new issue for that.
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