integral of a matrix

Question

raha ahmadi 2021-6-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/860180-integral-of-a-matrix

评论： raha ahmadi 2021-6-19

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

I want to take the integral of an exponetial of a matrix but I got this error and dont know how fix it:

'Unable to perform assignment because the indices on the left side are not compatible with the size of

the right side.

Error in Untitled7 (line 12)

ggg(ss)=integral(fun,0,T,'ArrayValued',true);'

thanks in advance

clc
clear 
close all
M=ones(3,3);
Dmat=[1;2;3];
fun=@(t)expm(-M.*t)*Dmat;
T=1e-2;
g=integral(fun,0,T,'ArrayValued',true);

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Walter Roberson 2021-6-19

And when you do not have that (ss) in there, then no error message is emitted.

I notice your tags mention expm, which is the matrix exponential, but your code uses exp() which is element-by-element exponential.

raha ahmadi 2021-6-19

two mistakes in 5 lines code! good for me !!

I m really sorry and thank you very much. I m very tired and ...I corrected it

I hope you best wishes

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Answer 1

Walter Roberson 2021-6-19

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https://ww2.mathworks.cn/matlabcentral/answers/860180-integral-of-a-matrix#answer_728340

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format long g
M = ones(3,3);
Dmat = [1;2;3];
fun = @(t)expm(-M.*t)*Dmat;
T = 1e-2;
g = integral(fun,0,T,'ArrayValued',true);
g
g = 3×1
       0.00970297763432788
        0.0197029776343279
        0.0297029776343279

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raha ahmadi 2021-6-19

I appreciate your attention and hope you all best

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Answer 2

Scott MacKenzie 2021-6-19

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https://ww2.mathworks.cn/matlabcentral/answers/860180-integral-of-a-matrix#answer_728305

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You note:

I want to take the integral of an exponetial of a matrix

But,

exp(-M.*t)*Dmat;

is a vector, not a matrix. Try using the dot operator in your function definition:

exp(-M.*t).*Dmat;

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raha ahmadi 2021-6-19

Dear Scott MacKenzie

sorry you are right but in fact I need to calculate the integal of a multiplication of a exponensial of a matrix by a column vector "Dmat". Its a matrix multiplication not an element-wise multiplication.

Best regards

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