Calculate improper integrals using while loop

Question

Rascad 2014-10-13

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/158460-calculate-improper-integrals-using-while-loop

编辑： Jane Kim 2014-10-14

Hello! I need some help. I am trying to use a while loop and int to calculate the integral of f(x) over the interval [a,b] for b = a, a + 1, a + 2, ... until successive integrals differ by less than some small number. Can somebody evaluate my code and let me know where problems may be? Thanks!

Also, I'm not returning any error messages... Just not returning the correct answers.

   function a = myimproperintegral(f, a, tol)
syms x;
m=0;
n=0;
b=a;
while (tol < abs(m-n))
    m=int(f(x), a, b);
    b=b+1;
    n=int(f(x), a, b);
end
a=n;
end

Here is the sample data:

a = myimproperintegral(@(x) 1/x^2,2,0.01)
a = 0.40909090909090909090909090909091
a = myimproperintegral(@(x) -1/x^3,3,0.001)
a = -0.051423324150596877869605142332415
a = myimproperintegral(@(x) 2*exp(-x),log(3),0.02)
a = 0.66217470200060977357189425877572
a = myimproperintegral(@(x) x^(-1.1),1,0.1)
a = 1.9725843823976931790483046193628

Any advice is much appreciated!

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Answer 1

Jane Kim 2014-10-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/158460-calculate-improper-integrals-using-while-loop#answer_155130

编辑：Jane Kim 2014-10-14

All you have to do is define m and n before the while loop. Instead of equating them to 0, use what you put in the while loop to define the two variables (e.g. m=int(f(x), a, b); n=int(f(x), a, b);). Watch the value of b.

If you don't, then t-s=0 automatically, so the function isn't going to do what you want it to do.