Find if point lies within n circles

I have a problem where I am trying to find which of the points in iv1 of code below lies within all the circles specified by C(it stores the centres of n circles, nx2 matrix). My code is shown below:

function [ctv]=ctrivec(iv1,c,r)
ctv=zeros(3,2);
n=size(iv1,1);
count=1;
flag=0;
for i=1:1:n
  flag=findptin(iv1(i,:),c,r);
  if flag==1
      ctv(count,:)=iv1(i,:);
      count=count+1;
  end
end
end

function [f]=findptin(p,c,r)
n=size(c,1);
f=1;
for i=1:1:n
  t=(p(1)-c(i,1))^2+(p(2)-c(i,2))^2-r^2;
  if t>0
      f=0;
      return;
  end
end
end

I am supposed to get three coordinates a smy output in the ctv vector(incidentally ctv stores the coordinates of the circular triangle formed by the intersection of 3 circles(the area of intersection to be specific)). However, I am not getting the desired outputs.

Example - consider the given case c=[3 5;7 2;2 2];

iv1 =

    4.5000    0.3417
    4.5000    3.6583
    4.9187    2.6938
    0.0813    4.3062
    5.9950    4.8266
    4.0050    2.1734

For this I should get the three points on ctv, but i am not getting it..

Pl help me out with this

P.S. I have not vectorized the code as i am not comfortable with this feature of MATLAB, I am more of a C programmer. Ignore this :)

Answer 1

[Saptarshi Bhattacharjee]

Update : I think the problem is because when I am computing the value of t from the line

t=(p(1)-c(i,1))^2+(p(2)-c(i,2))^2-r^2;

the output is coming as

   t =

1.6813e-004

I think this is making the problem during the check and that's why the points are getting omitted. Any idea why the result is i terms of e, and how can I change that to a normal value(as in decimal)??

[Walter Roberson]

format long g