Conditional entry-wise matrix operation

Hi, I am trying to compute the matrix 'Y' as follows with matrix 'X' as an input.

 If X_ij > 0
 then Y_ij = X_ij + log(exp(-X_ij)+1) 
 else Y_ij = log(1+exp(X_ij))

How do I implement this without any loops? Thanks.

Answer 1

[James Tursa]

Hints:

What does the expression -abs(X) do in relation to your condition of X_ij > 0? Could you use this in your formula for the calculation of Y?

Or, what if you created a logical indexing variable for your condition, such as g = X > 0. Can you think of how to use g as an index to calculating the appropriate elements of Y?

[Deepayan Bhadra]

I got it, thanks to logical indexing!