Can someone help implement the perfect shuffle function?

function outString = perfectMShuffle(inString,m)
% This function shuffles the characters in the inString by picking 1st,
% m+1st, 2m+1st characters till it reaches the end, then picking 2nd, m+2nd
% 2m+2nd etc.
% Examples:
%  perfectMShuffle('abcdef',3) -> 'adbecf'
%  perfectMShuffle('abcdef',2) -> 'acebdf'

Here is what I have so far, I might be totally wrong but thats what I tried

N = length(inString)/2;
y = zeros(N,1);

for k = 1:N

     y(2*k-1) = m;
     y(2*k) = N+k;
  end

Answer 1

[Jos (10584)]

x = 'ABCDEFGHIJKL' 
m = 3
% the following line pre-allocates an output to store things in, makes things faster!
y = x ; 
y(:) = '.' % for display purposes only
N = numel(x)
for k=1:m-1
    % there are m-1 positions where we have to begin in x
    ix = k:m:N % indices into X
    iy = (1:numel(ix)) + (k-1) % indices into y
    y(iy) = x(ix) % copy
end