根据另一个矩阵中相应元素的值更改矩阵中的元素

Question

First of all I want to generate a random matrix which size is the same as the input matrix. If an element value in random matrix is greater than 0.5 , then l have to increment the value of corresponding element in the input matrix by one, else decrement by 1.

X=[4       5        6  ;    7       8        9   ;     3        2       1]
Random=[ 0.65     0.43     0.23   ;       0.75     0.12      0.78  ;    0.31     0.96       0.58] 

Answer 1

You can use logical indexing to create a matrix of true values where Random is greater than 0.5 and false otherwise.

Random = rand(size(X));
greater_than_one_half = Random > 0.5;

You can then use this logical matrix to select and manipulate certain elements of X or Y .

% Add one to all values in X where Random > 0.5
X(greater_than_one_half) = X(greater_than_one_half) + 1;

% Subtract one from all values in X where Random <= 0.5
X(~greater_than_one_half) = X(~greater_than_one_half) - 1;

Or you could do something clever and use the negation ( ~ ) of the logical array as an exponent for -1 such that when it's false (0), it's -1 ( -1^(~0) ) and when it's true (1), it's 1 ( -1^(~1) ). Then add this to X .

X = X + (-1).^(~greater_than_one_half);

Or simply:

X = X + (-1).^(Random <= 0.5);