How to optimaze for loop

Hello.

I have this for loop.

[rows,cols]=size(A);
for i=1:1:rows

          this_col=A(i:rows,i);

          this_col_abs=abs(this_col);

           [max_value,max_position]=max(this_col_abs);

          max_position=max_position+i-1;

          if max_position~=i

              max_row=A(max_position,i:cols);
              max_row_val=B(max_position);

              A(max_position,i:cols)=A(i,i:cols);
              B(max_position)=B(i);

              A(i,i:cols)=max_row;
              B(i)=max_row_val;
          end

          ss=A(i,i);
          A(i,i:cols)=A(i,i:cols)/ss;
        B(i)=B(i)/ss;

          B(i+1:rows)=B(i+1:rows)-B(i)*A(i+1:rows,i)/A(i,i);
          A(i+1:rows,1:cols)=A(i+1:rows,1:cols)-A(i+1:rows,i)*A(i,1:cols)/A(i,i);

      end

How can I optimaze this loop;

[James Tursa]

Instead of your readers trying to read your undocumented code and trying to figure out what it is doing, maybe you could give us a description of what the input is and the desired output, and how you are currently going about it. Commenting your code is generally a very good practice.

[per isakson]

• See Profile to Improve Performance
• Nearly all the time is spent in the last line, A(i+1:rows,1:cols)=A(...

Answer 1

[Andrei Bobrov]

M = [A,B];
[m,n] = size(M);
for ii = 1:m
    D = M(ii:m,ii:n);
    [~,k] = max(abs(D(:,1)));
    D([1,k],:) = D([k,1],:);
    D(1,:) = D(1,:)/D(1,1);
    D(2:end,:) = D(2:end,:) - D(2:end,1)*D(1,:);
    M(ii:m,ii:n) = D;
end