# Mexican Hat function plot help

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Jesse on 5 Oct 2011
Hello all,
I'm trying to plot a certain Mexican Hat function (other than the one they provide in MATLAB), but I'm getting the matrix dimensions must agree when I define psi. I tried everything to fix the code, but no luck. Can someone advise?
I know some code is repetitive, but I need them in other areas of my code.
dXs = 1;
x = [-20,20];
SamplingScale = [1, dXs, 4, 20 ,40];
Range = SamplingScale;
HalfRange = Range/2;
Sigma = HalfRange/4;
SigmaSq = Sigma.^2;
for i = 1:length(x)
psi = (2/(sqrt(3)*Sigma)*pi^(-0.25))*(1-(i^2/Sigma^2))*(e^(-i^2/2*SigmaSq));
end
plot (psi)
Thanks again!

the cyclist on 5 Oct 2011
I did two main things with your code (pasted below):
1. Added a lot of "dot''s to the line of code in your loop. When you have vectors, and you want to do operation on those vectors element-by-element, you need to add those dots, so that MATLAB does not think you want to do matrix operations (e.g. matrix multiply or matrix inverse).
2. Added the line "e = exp(1)" to your code. MATLAB does not have "e" predefined. You could also have used the exp() function instead of your syntax.
You might want to read the "Getting Started" guide: http://www.mathworks.com/help/techdoc/learn_matlab/bqr_2pl.html
dXs = 1;
x = [-20,20];
SamplingScale = [1, dXs, 4, 20 ,40];
Range = SamplingScale;
HalfRange = Range/2;
Sigma = HalfRange/4;
SigmaSq = Sigma.^2;
e = exp(1);
for i = 1:length(x)
psi = (2./(sqrt(3)*Sigma)*pi^(-0.25)).*(1-(i^2./(Sigma.^2))).*(e.^(-i^2./(2*SigmaSq)));
end
plot (psi)
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Jesse on 5 Oct 2011
Hmm, apparently I didn't try everything!
Thanks cyclist!

### More Answers (1)

Palguna Gopireddy on 31 Mar 2022
What is the mexihat equation used in matlab. In original equation there is no term called [lb,ub].
Palguna Gopireddy on 8 Apr 2022
Thanks.Got it.any function can be know seen by pressing right click on it and opening it.
But for chebwin function one of the lines is 'chebwinx' which can't be opened. They said it is a MEX file. Do you know any way to open and see a MEX file in matlab.