Operations depending on the row/column

I have a 339x339 matrix (f2) containing values and I need to multiply all the cells below row 170 and columns less than 170 by -1. Below is what I have so far.

for t=1:339

if t < 170

f2=f2*-1;

end

end

This just makes everything negative.

Thank you for your help!

Answer 1

[madhan ravi]

 f2(1:169,:) = -f2(1:169,:)