Set elements in a 3D array to zero based on a condition

Hello,

I am trying to set all entries in a 3D array that are less than 0 to be equal to 0. My variable Qr is 199x199x50.

I tried this with no success:

Qr(Qr<0)==0

Answer 1

[Matt J]

Qr(Qr<0)=0;

Answer 2

[Matt J]

Qr=max(Qr,0);