Obtaining integral function from code

Question

john_arle 2019-6-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/467934-obtaining-integral-function-from-code

回答： Star Strider 2019-6-19

采纳的回答： Star Strider

在 MATLAB Online 中打开

Hello there!

I am trying to obtain the integral function of a complicated relation.

Here though, to check out the code, I am implementing the integral of f(x) = x.

However, I get an error when the index i of my function reaches 0.7.

Could please tell me why?

Thanks,

Have a good day.

Andrea.

MAIN:
x = [0:0.1:1];
prova = @(x) x;
figure
res(1:end) = fun_integra(prova, 0, 1, 0.1);
plot(x,prova(x))
figure 
plot(x, res(1:end))
FUNCTION fun_integra
function [res] = fun_integra(integrand, low, up, step)
    for i=low:step:(up-step)
        res((i-low)/(step)+1) = integral(integrand, low, i+step);
    end
end

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Answer 1

Star Strider 2019-6-19

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/467934-obtaining-integral-function-from-code#answer_379958

在 MATLAB Online 中打开

At that value, the subscript is no longer an integer. This is most likely a problem with floating-point calculation error. Using the fix (link) function to force the subscript to be an integer corrects it:

res(fix((i-low)/(step)+1)) = integral(integrand, low, i+step);

That leaves the problem of ‘x’ and ‘res’ not being the same lengths in:

res = fun_integra(prova, 0, 1, 0.1);

fixed by :

plot(x(1:numel(res)), res(1:end))