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arraysintegrationmaxima

Maxima: integration of `charfun` containing array items

If I run the following code

q: charfun(x>a);
assume(a<b);
integrate(q,x,a,b);

Maxima is able to compute the value of integral, which is b-a, but if I run the same calculation using items from an indexed array x[i] and x[i+1] in place of a and b, as below,

q: charfun(x>x[i]);
assume(x[i]<x[i+1]);
integrate(q,x,x[i],x[i+1]);

Maxima is not able to perform the symbolic computation and returns

enter image description here

instead of x[i+1]-x[i]. Is there a way to make Maxima calculate the integral?

Solution

  • Well, I think Maxima is getting confused that the variable of integration x also appears in the limits of integration. If you change the variable of integration to be something else, you get the expected result, I think.

    q: charfun(u>x[i]);
assume(x[i]<x[i+1]);
integrate(q,u,x[i],x[i+1]);

    yields x[i+1]-x[i].