2 different for loops at the same time ?

Hi, I've just tried to make 2 for loops at the same time but I couldn't achieve that properly. Assume that "A" can be any matrix. I upload example.xlsx file as an .txt file.

      A = xlsread('example.xlsx');
        for ii= 5:5:length(A);
     for  jj= 4:5:length(A);
     M=A(ii,11)*(10^A(jj,1))
     end
        end

When I try this code I get 16 M as an answer, I want to take 4 answers. Does anybody have any clue that can help ?

Answer 1

[Walter Roberson]

      A = xlsread('example.xlsx');
      iivals = 5:5:length(A);
      jjvals = 4:5:length(A);
      numii = length(iivals);
      numjj = length(jjvals);
      M = zeros(numii, numjj);
      for ii_idx = 1 : numii
        ii = iivals(ii_idx);
        for jj_idx = 1 : numjj
          jj = jjvals(jj_idx);
          M(ii_idx, jj_idx) = A(ii,11)*(10^A(jj,1))
        end
      end

[Gökçe Öter]

Thanks for your effort and quick answer also but with this code i get 16 matrix answers, I just want to get 4 value as an answer which are multiplication of two elements of A matrix.

[Walter Roberson]

     A = xlsread('example.xlsx');
     for ii= 5:5:length(A);
       M( ii/5 ) = A(ii,11) * (10^A(ii-1,1))
     end

[Gökçe Öter]

Thank you so much !

Answer 2

[Majid Farzaneh]

Hi, It's better use size(A,1) [for number of rows] or size(A,2) [for number of columns] instead of length(A). Because it's may not exactly what you want. At the M=A(ii,11)*(10^A(jj,1)) if you want to multiply values element by element you should use '.*' instead of '*'.

for ii= 5:5:size(A,1);
     for  jj= 4:5:size(A,1);
         M=A(ii,11).*(10^A(jj,1))
     end
end

[Gökçe Öter]

Thanks for your effort, but with this code i get 16 matrix answers, I just want to get 4 value as an answer

0.1312*1.0e+24     0.3681*1.0e+24     0.6380*1.0e+24     0.4334*1.0e+24

which are multiplication of two elements of A matrix.

Answer 3

[Rik]

You must index M.

jj_= 4:5:length(A);
ii_= 5:5:length(A);
A = xlsread('example.xlsx');
M=zeros(numel(ii),numel(jj));%pre-allocate
for ii=1:numel(ii_)
    for  jj=1:numel(jj_)
        M(ii,jj)=A(ii_(ii),11)*(10^A(jj_(jj),1));
    end
end

Answer 4

[Ameer Hamza]

You don't need a for loop. Replace it with this:

    M = A(5:5:length(A), 11).*10.^(A(4:5:length(A), 1));

This will work in R2016b and later.

[Gökçe Öter]

Thank you so much, but this code gives

1.0e+24 *

      0.1312    0.1312    0.1312    1.3120
      0.3681    0.3681    0.3681    3.6810
      0.6380    0.6380    0.6380    6.3800
      0.4334    0.4334    0.4334    4.3340

But I want to get an answer as

0.1312*1.0e+24     0.3681*1.0e+24     0.6380*1.0e+24     0.4334*1.0e+24

[Ameer Hamza]

Since you didn't give the dataset so it is hard to see what you want. But try the updated statement.

[Gökçe Öter]

My data set is messed up but I upload this if you want to look at it.

[Ameer Hamza]

As you can see, that your final answer is the first column of of 4x4 matrix. So you can get it like this

M = A(5:5:length(A), 11)*10.^(A(4:5:length(A), 1))';
M = M(:,1);

It will give you your required 4 numbers