MATLAB: Decrease the least and increase the highest

arraydecreasedivideincreasemultiplysign

I have an array

A = [1 -3 -6 10 2 3 7 -1 -9 -3]

B = [1 2 3 4 5 6 7 8 9 10]

1) I want to check the least negative and the highest positive in array A.

2) In the corresponding number in Matrix B, if it is the least negative then multiply the number in B by 10 and if it is the highest positive, then multiply the number in B by 100.

3) Then B = [1 2 3 400 5 6 7 8 90 10]

Best Answer

A = [1 -3 -6 10 2 3 7 -1 -9 -3];
B = [1 2 3 4 5 6 7 8 9 10];
[~,idxlo] = min(A);
[~,idxhi] = max(A);
B(idxlo) = 10*B(idxlo);
B(idxhi) = 100*B(idxhi)
B =
     1     2     3   400     5     6     7     8    90    10

Related Solutions

MATLAB: Is it possible to extract the values with a vector of indices for each row without using the for statement from the matrix

see sub2ind()

A = [1, 2, 3; 4, 5, 6; 7, 8, 9; 10, 11, 12]; % reference matrix
b = [2; 1; 1; 3]; % index for each row that I want to extract
idx = sub2ind(size(A), 1:size(A,1), b.');
A(idx)

Result

>> A(idx)
ans =
     2     4     7    12

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

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.

Best Answer

Related Solutions

MATLAB: Is it possible to extract the values with a vector of indices for each row without using the for statement from the matrix

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

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