## extend a Matrix in every iteration

### Fernando Arias (view profile)

on 18 May 2018
Latest activity Edited by jonas

on 18 May 2018

### Stephen Cobeldick (view profile)

Hi, I'm having some problems with my code. I have a 3 dimension matrix in which index represent a coordinate, for example, a 10x10x10 array where the first index are 1, 1, 1 represent the point x=1, y=1 and z=1. And the value in the array represent the number of points in theese coordinates. Now I want to use ptCloud function, so I have to extract all the points from my array. What I'm trying is this (If I were in the case 10*10*10 matrix A):
MAT=[]
for i=1:1000
[Yj Xj Zj]=ind2sub(size(A), i);
value=A(Yj Xj Zj);
P=[Yj Xj Zj];
P2=repmat(P,value,1)
MAT=[MAT;P2]
end
With this code I already have a matrix MAT whith every points. But the case is that my array is 200x200x160, and I noticed that in every iteration the time that the code requires increases a lot, so I think there would be something wrong in the for loop.
Thanks so much.

jonas

### jonas (view profile)

on 18 May 2018
The time for every iteration increases due to the size of MAT increasing with every iteration (can be fixed by preallocation). I don't understand what the desired output is, but I'm guessing there is a more effective way than a loop. What is MAT describing?
Fernando Arias

### Fernando Arias (view profile)

on 18 May 2018
MAT is the matrix wich contains all points, for example, if there is a 3 in A(1,1,1) means that I have three points in (1,1,1) so I add 3 rows of [1, 1, 1] to the matrix MAT. Finally I would like to have a matrix with all points where first colum is x coordinate, seconx y and third z.
I think there would be another way quiker, becouse with this code I can't have the matrix in more than a day.
jonas

### jonas (view profile)

on 18 May 2018
EDIT: nvm, Mr. Cobeldick solved that beautifully

### Stephen Cobeldick (view profile)

on 18 May 2018
Edited by Stephen Cobeldick

on 18 May 2018