MATLAB: How to modify a matrix to change the entries >=0 and multiply it by 5 AND to change the entries <0 and add 2 to those entries

homework

I have tried the following: function [A] = modify_matrix(a,n,m)
    if (a>=0)
        A(i,j) = a(i,j)*5;
    end
end
function [A] = modify_matrix(a,n,m)
    if (a<0)
        A(i,j) = a(i,j)+2;
    end
end
The question is:
1. If an entry in B is greater than or equal to zero then multiply it by 5
2. If an entry in B is less than zero then add 2 to it.
Then use this new function to create a matrix A obtained by modifying the following 30 × 30 matrix B (which you can copy and paste directly into Matlab). Then find the determinant of A
B = [5 10 -4 8 -6 -6 -2 5 -4 8 1 -5 -1 -1 -3 -3 3 -2 -8 1 9 3 1 -4 3 9 7 9 3 9;-4 -6 -6 -5 3 5 -0 8 9 -4 -2 -4 7 9 4 2 -9 4 2 8 4 6 9 2 5 6 8 -6 -7 6;4 -2 3 -9 5 -9 4 -2 9 -2 -6 10 -3 -2 -9 5 9 -8 2 -2 7 -2 5 9 5 -5 -1 -8 10 6;-1 10 -4 8 5 1 4 -10 4 3 5 -3 4 1 -9 -7 -2 -6 -8 1 2 -3 -6 -5 -7 5 0 -3 -3 -9;0 7 2 2 -3 8 -7 -10 -5 0 -9 -4 -6 3 -9 5 4 -2 -4 -0 1 3 -2 0 -3 -3 1 -7 8 -6;2 4 -8 -4 -9 -6 8 -2 -3 4 1 -6 -9 -4 9 4 -9 -9 1 10 3 -7 -3 6 7 5 -1 2 1 -9;10 -9 -8 -8 -2 1 -1 2 -8 2 2 -8 -1 2 5 -3 9 3 0 -7 -1 6 -8 -0 -5 6 -9 4 -4 4;-2 9 -5 0 8 5 4 -1 5 -8 1 7 5 10 2 -7 6 8 7 9 4 -5 -8 4 -7 -2 -3 0 0 -10;-5 6 -0 4 -7 1 -4 9 -3 4 -10 -8 -1 -7 -5 3 -8 -10 -2 9 3 -2 8 -2 8 -9 -7 -6 2 0;-8 1 0 4 -10 6 -5 1 2 -7 -5 6 -5 2 5 -4 -0 4 2 4 2 -10 1 -1 -3 8 -7 1 3 3;-4 -3 -9 -8 -5 7 -10 -6 8 9 -7 8 2 -9 3 -0 -6 8 6 1 4 -8 -10 -10 -8 -5 -1 3 4 -9;-3 3 10 -9 -0 -0 8 7 7 -7 -9 7 -4 4 -3 4 -9 -5 10 6 -3 8 -9 10 0 -1 -9 -6 7 3;0 -1 -6 -4 -2 -7 2 4 0 -3 2 9 -4 1 7 -1 8 4 8 -10 -5 -5 -1 5 -7 8 -9 -0 -6 10;-5 2 -4 -10 0 -5 2 -1 6 1 -3 8 -7 -6 7 10 -6 -10 6 -7 7 -9 0 2 5 1 7 -2 -3 -5;-8 -3 7 -2 3 -3 1 -6 -9 -9 0 -1 4 6 8 -8 9 1 2 -1 -5 -6 -6 -2 -9 -10 -1 0 -10 6;0 -7 9 8 7 1 3 -8 8 -0 -3 3 3 -4 -9 -7 -7 -7 -2 -7 5 4 -3 -1 -5 2 -7 3 1 4;8 -6 6 -1 3 -2 3 -3 -4 7 -1 -10 4 8 -0 -3 -4 9 5 5 -6 -7 -8 -4 5 -5 -6 3 -9 5;-6 -6 5 6 -3 5 3 -9 4 -2 -1 -9 -2 7 -6 7 3 -9 8 4 -5 -2 -5 3 -4 -5 -5 4 -1 -2;5 10 -6 3 8 1 5 -8 8 10 2 9 -4 -6 -8 8 9 -1 6 -7 -6 0 -8 -9 8 1 2 8 3 -6;-4 7 1 6 9 -6 -2 7 9 5 7 10 6 -7 -3 -4 -2 -8 5 -9 4 2 -5 1 -5 2 -8 1 -8 -5;-5 1 -4 3 -5 0 7 10 7 5 7 3 -2 -10 -1 -2 4 -3 5 -2 6 3 9 9 -1 9 3 8 7 5;4 -9 5 -4 -4 1 4 5 9 -7 -4 4 -2 8 -1 5 7 -10 7 9 -5 -0 -4 -1 7 3 2 -5 9 4;8 -5 -8 6 3 -2 8 8 2 -10 9 -5 6 -3 1 -1 3 -3 -8 -4 7 3 8 -7 -10 0 -4 6 8 -8;-3 3 1 2 8 -5 -6 -6 -8 -10 -7 3 -4 7 -0 -4 8 9 -5 3 3 -0 -5 3 -9 5 -6 -3 -4 9;-0 -6 -7 -8 -7 -3 -1 -4 5 -10 4 -1 7 0 8 8 -2 2 8 8 -6 1 -9 -6 3 -2 -3 5 6 -1;-1 7 1 -1 -3 7 5 8 5 8 5 0 6 3 -8 -5 -7 -6 5 2 -7 8 6 9 -4 -4 -7 -3 2 4;5 -4 2 -3 -1 6 4 -8 -0 6 -9 -8 -1 -8 9 1 -4 10 5 9 7 9 -0 6 -4 6 1 -5 2 -1;-1 8 6 3 -7 0 2 8 8 -1 2 1 -6 -0 1 -1 7 -1 9 -1 -9 -6 -4 6 -4 7 3 2 4 -9;-3 -4 -3 -2 8 -9 -9 -5 -1 -2 2 1 3 1 7 4 9 6 -10 -4 3 -9 3 -4 -2 8 7 -3 8 1;-8 -4 -3 1 -7 -5 -2 -9 2 7 -7 0 4 7 -8 -6 -5 -5 -4 4 1 6 -2 -1 5 -10 0 -2 9 -10]

Best Answer

Start with "If an entry in B is greater than or equal to zero": You can either run a loop over all elements of B or use "logical indexing":
% Linear indexing:
for k = 1:numel(B)
   if B(k) >= 0
     ...
   end
end
Or two indices for rows and columns:
for r = 1:size(B, 2)
  for c = 1:size(B, 1)
    if B(r, c) >= 0
       ...
    end
  end
end
Or "logical indexing":
index = (B >= 0);
disp(B(index))
Now try to use this to modify B. Use the mentioned terms to search in the documentation and in the internet.
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