Correlation using for loop

Dear all,

I have 2 matrices, M_ET [3700 12] and M_Compiled [7400 12]. Using a for loop, I want to do the following:

1. Correlate [100 12] of M_ET with [100 12] M_Compiled to get [1 12] of values stored in C_ET.
2. Repeat 1. for the remaining rows of M_ET and M_Compiled, where rows increase by 100.

C_ET(1,:)     = diag(corr(M_ET(1:100,:), M_Compiled(1:100,:)));
C_ET(2,:)     = diag(corr(M_ET(101:200,:), M_Compiled(101:200,:)));
C_ET(3,:)     = diag(corr(M_ET(201:300,:), M_Compiled(201:300,:)));

My C_ET should therefore be [74 12]. However, my C_ET is instead giving me [1 12]. Any help is greatly appreciated. Thank you.

% M_ET = [3700 12]
% M_Compiled = [7400 12]
% C_ET = [37 12]

for row = 1:100:7400
    for r = 1:100:3700
    row1 = row; 
    row2 = row + 99;
    r1 = r;
    r2 = r1 + 99;
    C_ET(:,:)     = diag(corr(M_ET(r1:r2,:), M_Compiled(row1:row2,:)));
        end
end

[Steve Eddins]

I'm not sure specifically what you are trying to compute, but I noticed something odd about your loops. The matrix C_ET is being completely and independently replaced each time through the loops. The result will be that only the final trip through the inner loop body has any effect.

[Elizabeth Yeap]

Hi @Steve Eddins, that does seem to be the case. Any ideas on how to correct this error? Thank you for your help!

[KALYAN ACHARJYA]

If you describe the question with a sample example, it will be easier to answer.

• What do you have?
• What are you trying to do?

[Elizabeth Yeap]

Hi @KALYAN ACHARJYA, I have tried to provide further explanations.

Answer 1

[KALYAN ACHARJYA]

Problem, you are trying to access the rows to 7400, but the rows in M _ET [3700 12] have a maximum of 3700, as

M_ET [3700 12] 
M_Compiled [7400 12]

If you manage to provide enough rows to the M _ET data matrix, there will be no problem

C_ET=cell(1,74);
l=1;
for i=1:100:7400-99
  C_ET{l}=diag(corr(M_ET(i:i+99,:), M_Compiled(i:i+99,:)));
  l=l+1;
end 
C_ET=cell2mat(C_ET);

Verify

>> whos C_ET
  Name       Size            Bytes  Class     Attributes
  C_ET      12x74             7104  double        

[Elizabeth Yeap]

Thank you!