Searching for help on matlab : Warning: Explicit integral could not be found

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Shaymaa
Shaymaa 2013-12-26
编辑： Roger Stafford 2013-12-27
Hello,
I'm trying to solve definite integral on MATLAB, but there is always an Error Message: Warning: Explicit integral could not be found.
The function include syms x y
f= -exp(-(249*(x + (15*y)/83 - 105/83)^2)/(25*(y/250 - 7/250)))/(y - 7)
>> int(f,y,0,7) but the following message occurs Warning: Explicit integral could not be found.

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回答（2 个）

Walter Roberson
Walter Roberson 2013-12-26
Not every integral has a closed algebraic form. You are probably going to have to use numeric integration.
What kind of value are you expecting for "x" ? Your integral gets into large values very very quickly. The division by (y-7) is not going to do you any numeric favors as y goes to 7.
Roger Stafford
Roger Stafford 2013-12-27
编辑：Roger Stafford 2013-12-27
As it stands, this integral is divergent at its upper limit of integration. It's no wonder the warning was issued. The argument of 'exp' is always positive as y approaches 7 from below, so the value of exp(...) is always greater than or equal to one. The indefinite integral of 1/(y-7) would be log(7-y) which becomes minus infinity as y approaches 7, so the same holds true of this integral.

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