array of vector positions Matlab

Question

I'm trying to create a cloth simulator and need a way of storing the particle positions. I would like to store them as [x,y,z]. I need an array for the all the particle positions. This would mean having an array [[x1,y1,z1],[x2,y2,z2],...etc].

My width and height are both 3, so there should be 9 [x,y,z]'s in the grid. However my output shows 100s of positions. I don't really know what it is I'm doing wrong. Sorry if this question could be formatted better.

for i = 1:particleWidth
    for j = 1:particleHeight
        X = (width*(i/particleWidth));
        Y = (height*(j/particleHeight));
        xPos = [xPos,X];
        yPos = [yPos,Y];
    end
end

[T1,T2,T3] = ndgrid(xPos,yPos,Z);
grid = [T1(:),T2(:),T3(:)];
disp(grid);

Answer 1

ndgrid replicates the inputs in order to create a grid.

[X,Y]=ndgrid(1:3,4:6)

X =

     1     1     1
     2     2     2
     3     3     3


Y =

     4     5     6
     4     5     6
     4     5     6

If want to use that function, you should initialize xPos and yPos as vectors :

xPos = (width/particleWidth).*(1:particleWidth);
yPos = (height/particleHeight).*(1:particleHeight);
[T1,T2] = ndgrid(xPos,yPos); %T1 and T2 will be width-by-height arrays
grid = [T1(:),T2(:),zeros(numel(T1),1)]; % Or whatever Z should be

Basically, you had already created xPos and yPos as arrays with width x height entries, so you get at least the square of that number out of ndgrid . If Z also have 9 elements, that would make 9^3 = 729 rows out.