MATLAB: Change 1 to -1 in a matrix

change 1 to -1 in a matrix

Hi to all the members, I have a 4 X 4 Matrix of one i.e ones(4). I want to change all the elements from 1 to -1 randomly in the matrix. BUT Only one element should change at a time from 1 to -1. That it the 1 changes to -1 sixteen times as we have sixteen elements in the matrix.

Best Answer

m = ones(4);
r = rand(4) - 0.5;
m = m .* sign( r );

is one of many ways to do it.

Related Solutions

MATLAB: Randomly change signs of certain elements in a matrix

Do NOT use a loop for this! You can do this very simply with logical indexing:

>> a = [1,-1,1;1,1,1;-1,-1,1]
a =
   1  -1   1
   1   1   1
  -1  -1   1
>> idx = randperm(numel(a),4);
>> a(idx) = -a(idx)
a =
  -1  -1   1
   1   1   1
   1   1  -1

You can even randomly pick 3 or 4 elements:

   idx = randperm(numel(a),randi([3,4]));

For versions prior to R2011b you will need to return the entire vector and select from that:

vec = randperm(numel(a));
idx = vec(1:4);
a(idx) = -a(idx)

MATLAB: How to select two number randomly from an array and perform swapping between these two number

    A=[1 2 3 5 6 9 10] ;
    %%select two numbers and swap
%%using randsample
    idx = randsample(1:length(A),2) ;
    B = A ;
    B(fliplr(idx)) = A(idx) ;
    %%using randperm
  idx = randperm(length(A),2) ;
  B = A ;
  B(fliplr(idx)) = A(idx) ;

Best Answer

Related Solutions

MATLAB: Randomly change signs of certain elements in a matrix

MATLAB: How to select two number randomly from an array and perform swapping between these two number

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