I Keep Getting Error "Matrix dimensions must agree"

I keep getting error like

Error using .*

Matrix dimensions must agree.

How Can I fix it ? Please help me. Any help given will be much appreciated. Here is the line of code

[Adam]

You can fix it by ensuring the two sides of the multiplication are the same size. It's really that simple! We have no idea what size af is from the code you showed. You can see trivially in your workspace though so if you give all the information it is a lot easier for people to help.

Answer 1

[Nicolas B.]

If you are using *, than it is a matrix multiplication and the size of your matrices must be compatible.

If you want to multiply element per element, uses .* .

Examples:

a = [1 2 3];
b = [1 2 3; ...
     4 5 6; ...
     7 8 9];
c = [9 8 7; ...
     6 5 4; ...
     3 2 1];
 
a * b % result -> [30 36 42]
a * c % result -> [30 24 18]
a .* b % result -> [1 4 9
       %            4 10 18
       %            7 16 26] each value of a multiply all values of the same column in b
b .* c % result -> [ 9 16 21
       %            24 25 24
       %            21 16  9] multiply element per element

[Alexandra Keith]

But I have using .* and still error.

>> a=imread('tul.jpg');
>> lp=butterlp(a,15,1);
>> af=fftshift(fft2(a));
>> aflp=af.*lp;

[Nicolas B.]

what are the size of lp and af?