Integrate[DiracDelta[s (x - c)] x, {x, -Infinity, Infinity},
Assumptions -> {s > 0, c > 0}]
gives me c/s
in version 10.3.1, but 1+c+1/s
in version 10.4.1. Have I missed anything here?
Confirmed for 10.4.1 as Alexei. However, WolframAlpha still gives the c/s result.
And using the properties of Dirac delta function, I would say that c/s is the correct one. May be a bug of the new 10.4.1?
You can test with numeric constants, and Mathematica gives the correct answer. But symbolic result is wrong,
Integrate[DiracDelta[(x - 3)*2] x, {x, -Infinity, Infinity}]
gives 3/2.
Another test: it seems it only happens with this expression. This one,
Integrate[DiracDelta[s ( x - c/s)] x, {x, -Infinity, Infinity},
Assumptions -> {s > 0, c > 0}]
Gives the correct answer: c/s^2.
EDIT.- The new Mathematica 11 corrects this issue.
s!=0
$\endgroup$c/Abs[s]
) fors < 0
. But it should still work. (In fact, both integrals, withs > 0
ands < 0
, work fine in 10.2.0.) $\endgroup$