change even column values only

I create 20*20 2D array of all ones. And then I want to change even columns to minus one. How can I change with builtin function?

Answer 1

[Thorsten]

A = ones(20);
A(:,mod(1:20, 2) == 0) = -1;

[PK]

good answer! I got the following method.... A = ones(20) A(:,2:2:end) = -1

[Thorsten]

You method is even better!

Answer 2

[PK]

good answer! I got the following method.... A = ones(20) A(:,2:2:end) = -1