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error >> Matrix dimensions must agree. How to fix

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Ofer Aluf
Ofer Aluf 2024-4-23
编辑： Torsten 2024-4-23
Ran in:
Hello,
I have script:
d=0.025:0.0025:1; % d=0.125*Lambda to 12.5*Lambda
Lambda=1;
% Ga function
Lambda=0.2;l1= Lambda/4;zi=l1;si=1;k=(2*pi)/Lambda;
z=0:Lambda/400:Lambda/4;
y= sqrt(d.^2+(z-zi));
Arrays have incompatible sizes for this operation.
Gfun=@(z)(1./y).*exp(-1i.*k.*y).*exp(-1i.*k.*si.*z);
% R=sqrt(d^2+(z-zi));
% evaluate the integral from z=0 to l1
Ga=integral(Gfun,0,Lambda/4);
Question? Why i got message "Matrix dimensions must agree"? and how to fix it??

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回答（3 个）

Anjaneyulu Bairi
Anjaneyulu Bairi 2024-4-23
编辑：Anjaneyulu Bairi 2024-4-23
Hi,
Below line causing the error and it says "z" and "zi" are incompatible sizes for this operation.
y= sqrt(d.^2+(z-zi));
The "d.^2" variable has size of 1*391 double and "(z-zi)" has size of 1*101 double. Make sure you have declared these variables correctly to avoid these kind of errors.
You can refer below documentation links to know more information on arrays
https://in.mathworks.com/help/matlab/learn_matlab/matrices-and-arrays.html
https://www.mathworks.com/help/matlab/matlab_prog/compatible-array-sizes-for-basic-operations.html
I hope above information is helpful to resolve your query
Lokesh
Lokesh 2024-4-23
Hi Ofer,
It appears that you are encountering the error "Matrix dimensions must agree" while running your MATLAB script.
This issue arises because the dimensions of "d.^2" (1x391) and "z-zi" (1x101) in the equation "y= sqrt(d.^2+(z-zi));" are not compatible, leading to the error.
Please refer to the following MATLAB documentation for more information about compatible array sizes for basic operations:
https://www.mathworks.com/help/matlab/matlab_prog/compatible-array-sizes-for-basic-operations.html
Hope this helps!
Torsten
Torsten 2024-4-23
编辑：Torsten 2024-4-23
Ran in:
z doesn't need to be prescribed in array form because you integrate with respect to z. Here I assume that the integration variable and the z in the expression for y are the same.
If you mean to evaluate your integral for the d-values that you defined, you can use
d=0.025:0.0025:1; % d=0.125*Lambda to 12.5*Lambda
% Ga function
Lambda=0.2;l1=Lambda/4;zi=l1;si=1;k=(2*pi)/Lambda;
y= @(d,z)sqrt(d^2+(z-zi));
Gfun =@(d,z)(1./y(d,z)).*exp(-1i.*k.*y(d,z)).*exp(-1i.*k.*si.*z);
Ga=arrayfun(@(d)integral(@(z)Gfun(d,z),0,Lambda/4),d);
plot(d,[real(Ga);imag(Ga)])

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