Numerical integration Error in size of elements

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farzad 2014-2-11

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https://ww2.mathworks.cn/matlabcentral/answers/115772-numerical-integration-error-in-size-of-elements

编辑： Azzi Abdelmalek 2014-2-11

Hi all

I have a function to integrate , the problem is , for any amount of x that contains zero , the size of g matrix becomes one smaller , like x : 1x19 and g :1x18 , what happens to g when I calculate it's square root ??? what changes the dimension ? since this integration needs that x and g be of the same dimension

x=[-p/2:1:p/2];
f= c*sin(a/p*x);
g=sqrt(1+(diff(f)).^2);
integ=trapz(x,g)

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Answer 1

Azzi Abdelmalek 2014-2-11

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https://ww2.mathworks.cn/matlabcentral/answers/115772-numerical-integration-error-in-size-of-elements#answer_124034

编辑：Azzi Abdelmalek 2014-2-11

在 MATLAB Online 中打开

Because diff will reduce the length of g , use

integ=trapz(x(1:end-1),g)

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Azzi Abdelmalek 2014-2-11

Farzad commented

Thank you so much Azzi , just to know about it , why diff reduces the length ? and there is one other command : derivative , can it be used in this condition ? in general ?