Faster method of creating list of looped row vectors?

At the moment I have the following code:

kres=1;
kz=0;
K=[];

    for kx=-3:kres:3
        for ky=-3:kres:3
            k=[kx,ky,kz];
            K=[K;k];
        end
    end

to achieve a list of row vectors in the form:

[-3,-3,0;-3,-2,0;-3,-1,0;-3,0,0;....;3,2,0;3,3,0]

However when kres is reduced to < 0.01 this loop takes a long time to compute. Is there a faster way to achieve the same result without having to have a loop within a loop?

Answer 1

[Bjorn Gustavsson]

kres=1; kz=0; K=[]; This is the way I'd go about it:

x = -3:kres:3;
y = -3:kres:3;
z = 0;
[x,y,z] = meshgrid(x,y,z);
K = [x(:),y(:),z(:)];

HTH

[mfas]

That's perfect thanks!

Answer 2

[Keith Hooks]

You'll see quite a bit of improvement if you pre-allocate K. I understand the coding is not as clean, but the speed improvement is close to 5X for the 0.1 resolution.

Original: Elapsed time is 0.027472 seconds .

With pre-allocation: Elapsed time is 0.005479 seconds .

kres=.1;
kz=0;
kx = -3:kres:3;
ky = -3:kres:3;
n = length(kx);
m = length(ky);
K=zeros(n*m,3);

for i=1:n
    for j=1:m
        k=[kx(i),ky(j),kz];
        K((i-1)*n + j,:) = k;
    end
end

Answer 3

[Thorsten]

kres=0.01;
kx = -3:kres:3;
N = numel(kx);    
k1 = repmat(kx, [N 1]);
K2 = [k1(:) repmat(kx', [N 1]) repmat(0, [N^2 1])];