How to properly vectorize in Matlab - matlab

Question

I have a set a section of code that is taking a long time to run. I read over the vectorization page on the mathworks site. I am still a little confused on one part, is it possible to vectorize the part where I run plane_intersect?
Unvectorized
for N = 1:sizeDimages
imPos = anaInfoSat(N).ImagePositionPatient;
A2Z = imPos(3);
A2Y = imPos(2);
A2X = imPos(1);
[upP1(N,:)]=plane_intersect([cosSx(1),cosSy(1),cosSz(1)],[uppersatX1,uppersatY1,uppersatZ1],crossS,[A2X,A2Y,A2Z]);
[loP1(N,:)]=plane_intersect([cosSx(1),cosSy(1),cosSz(1)],[lowersatX1,lowersatY1,lowersatZ1],crossS,[A2X,A2Y,A2Z]);
end
My attempt at vectorization, the thing is upP1 is a Nx3 matrix. I preallocate the upP1 matrix. This code below returns an error about dimension mismatch. ImagePosition is a 1x3 matix.
N = 1:sizeDimages;
imPos = anaInfoSat(N).ImagePositionPatient;
A2Z = imPos(3);
A2Y = imPos(2);
A2X = imPos(1);
[upP1(N,:)]=plane_intersect([cosSx(1),cosSy(1),cosSz(1)],[uppersatX1,uppersatY1,uppersatZ1],crossS,[A2X,A2Y,A2Z]);
[loP1(N,:)]=plane_intersect([cosSx(1),cosSy(1),cosSz(1)],[lowersatX1,lowersatY1,lowersatZ1],crossS,[A2X,A2Y,A2Z]);
Here is part of the plane_intersect code, should be enough to let you know what it does.
function [P,N,check]=plane_intersect(N1,A1,N2,A2)
%plane_intersect computes the intersection of two planes(if any)
% Inputs:
% N1: normal vector to Plane 1
% A1: any point that belongs to Plane 1
% N2: normal vector to Plane 2
% A2: any point that belongs to Plane 2
%
%Outputs:
% P is a point that lies on the interection straight line.
% N is the direction vector of the straight line
% check is an integer (0:Plane 1 and Plane 2 are parallel'
% 1:Plane 1 and Plane 2 coincide
% 2:Plane 1 and Plane 2 intersect)
%
% Example:
% Determine the intersection of these two planes:
% 2x - 5y + 3z = 12 and 3x + 4y - 3z = 6
% The first plane is represented by the normal vector N1=[2 -5 3]
% and any arbitrary point that lies on the plane, ex: A1=[0 0 4]
% The second plane is represented by the normal vector N2=[3 4 -3]
% and any arbitrary point that lies on the plane, ex: A2=[0 0 -2]
%[P,N,check]=plane_intersect([2 -5 3],[0 0 4],[3 4 -3],[0 0 -2]);

Answer 1

In your vectorized code anaInfoSat(N).ImagePositionPatient; won't return a single, but several answers. If you assign the resuts to a single variable it will receive only the first answer. This is why you get dimension mismatch error.
Depending on the data class you can combine into a matrix
imPos = [anaInfoSat(N).ImagePositionPatient];
or into a cell array
imPos = {anaInfoSat(N).ImagePositionPatient};
You can also assign to several variables as the same time:
[A2X, A2Y, A2Z] = anaInfoSat(1:3).ImagePositionPatient;