Good evening everybody, the appended file shows an irritating (at least for me) behavior. Simplifying the integral of the title under the assumption that m and n are integers one gets 0. This is obviously wrong for m==n ! Is there a reason?

There is some discussion of this topic in the documentation [image] Mathematical Functions—Wolfram Documentation Mathematical functions in the Wolfram Language are given names according to definite rules. As with most Wolfram Language functions, the names are usually complete English wo…

Also, your sol2 seems to use the assumptions after the actual integration. This seems to work better: Integrate[Sin[n*Pi*x]*Sin[m*Pi*x], {x, 0, 1}, Assumptions -> {m \[Element] Integers, n \[Element] Integers, m == n}]

Thank you, Gentlemen for the fast and insightful response. Particularly that of Illian made me better prepared for similar situations.

[?] Integrate[Sin[x Pi n] Sin[x Pi m], {x,0,1}] for m=n ?

Questions

danl (Daniel Lichtblau) April 4, 2018, 11:10pm 4

This is largely a duplicate of a thread from last year .

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[?] Integrate[Sin[x Pi n] Sin[x Pi m], {x,0,1}] for m=n ?

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