azimuths between points on a plane

ola,

I'm using now atan2d to calculate azimuths (relative to east) on a plane between two grids, sized 970X1144:

for i=1:length(f)
    xx=x-x(f(i)); yy=y-y(f(i));
    az=atan2d(yy,xx);  
end

however, this method increases running time as it consumes 25% of it.

is there a less time-consuming way of doing this?