Mathematica v12 Integration bug?

Question

Bug introduced in 12.0 and fixed in 12.1

After upgrading to mathematica 12, this integral gives the wrong result, also with other types of similar integrals.

Integrate[t[2]*Exp[t[2]],t[2]]

The output

Exp[t[2]^2]/2

is wrong (it should be E^t[2] (-1 + t[2])). Such problem does not exist in previous versions.

PS, I have to use a lot of t[i] in my program, even if I change the [i] to subscripts, the problem is still there.

It is interesting to note that if I pick a variable without index, then it gives you what you expect. In other words, Integrate[blah*Exp[blah], blah] gives (-1 + blah) E^blah as you expect. OK, a new wrinkle: when using the t[2], I notice that it doesn't properly highlight the variables over which we are integrating. — Mark R
– Mark R, Commented Nov 8, 2019 at 0:30
Integrate[t[1] Sin[t[1]], t[1]] fails, but Integrate[t@Hold[2]*Exp[t@Hold[2]], t@Hold[2]] succeeds. — Michael E2
– Michael E2, Commented Nov 8, 2019 at 2:29

Nasser · Accepted Answer · 2020-03-18 18:16:09Z

8

Fixed in 12.1

Mathematica graphics

ClearAll[t]; Integrate[t[2]*Exp[t[2]], t[2]]

answered Mar 18, 2020 at 18:16

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