Question

I implemented the following function in Matlab.

function [x y] = cloud(a,b,phi,x0,y0,N)
phi=phi*2*pi/360;
m=ceil(5*N/pi);
x=a*(-1+2*rand(m,1));
y=b*(-1+2*rand(m,1));
f=sqrt(a^2 - b^2);
indexMatrix=zeros(m,3);
indexMatrix(:,1)=x;
indexMatrix(:,2)=y;
insidePointsMatrix=zeros(1,2);
j=1;
for i=1:m
    insidePoint=sqrt(((x(i)+f).^2) + (y(i))^2) + sqrt(((x(i)-f).^2) + (y(i))^2);
    if (insidePoint<=2*a)
        indexMatrix(i,3)=1;
        %insidePointsMatrix(j,:)=indexMatrix(i,1:2);
        if j<=N
            insidePointsMatrix(j,1:2)=indexMatrix(i,1:2);
            j=j+1;
        end
    end
end

I am reading about arrayfun and cellfun, and I am wondering if it is possible to shorten the function I already implemented using it. Given a 2 x n matrix A where (u,v) are the entries for any given row, how can I return a matrix listing the output of the following formula for each row?

sqrt((u+f).^2+v.^2) + sqrt((u-v)^2+v^2)

The variables f and a are defined above. I am trying to transform a series of points into an ellipse.

Answer 1

using find should give you the u,v coordinates:

cond=sqrt(((x+f).^2) + y.^2) + sqrt(((x-f).^2) + y.^2) ;
ind=find(cond<=2*a);
u=x(ind);
v=y(ind);