MATLAB: Finding the coordinates of multiple midpoints in an imported numerical matrix

Question

Hi, I'm new to matlab and have been stuck on this for awhile now.

I have a large numerical matrix dataset i imported into matlab. For the sake of my question we can use the magic(4) matrix.

EDU>> a = magic(4)

a =

    16     2     3    13
     5    11    10     8
     9     7     6    12
     4    14    15     1

I also found a function which I called and saved as midpoint:

function [mp] = midpoint(x1,y1,x2,y2) 
mp = [0 0]; 
mp(1) = (x1+x2)/2; 
mp(2) = (y1+y2)/2; 
return

To find a single value in the matrix the function works fine:

    EDU>> midpoint((a(1,1)),(a(1,2)),(a(1,3)),(a(1,4)))
ans =
      9.5000    7.5000

However the instant I try to calculate more than 1 midpoint at once I get an error:

EDU>> midpoint((a(1:2,1)),(a(1:2,2)),(a(1:2,3)),(a(1:2,4)))
   In an assignment  A(I) = B, the number of elements in B and I must be the same.In an assignment 
  Error in midpoint (line 4)
  mp(1) = (x1+x2)/2;

In my dataset I easily have to calculate more than 3000 midpoints. Is there a way to fix my current function or an alternative way to do this that allows me to calculate all the midpoints simultaneously

Thanks Kyle

Answer 1

Try this:

function test3
a =[...
    16     2     3    13
     5    11    10     8
     9     7     6    12
     4    14    15     1]
m = midpoint(a)  % Call the function
function [mp] = midpoint(arrayWith4Columns) 
x1 = arrayWith4Columns(:, 1);
y1 = arrayWith4Columns(:, 2);
x2 = arrayWith4Columns(:, 3);
y2 = arrayWith4Columns(:, 4);
mp = [x1+x2, y1+y2]/2; 
return

It gets the midpoint for all rows in the 4-column matrix.