Question

The following matrix:

A = [ -1 1 -1 1 -1 1 0 0 0 0 -1 1 0 0 -1 1 -1 1 0 0 ]

Would be like this:

A = [ -1 1           0 0 0 0 -1 1 0 0 -1 1      0 0 ]

Answer 1

Interesting little problem. I believe this works:

A = [-1 1 -1 1 -1 1 0 0 0 0 -1 1 0 0 -1 1 -1 1 0 0]; %# Set up an example vector
I1 = [1, 1, A(1:end-2) - A(3:end)]; %# Index all repetitions of sets of two using zeros
I1(A == 0) = 1; %# Ensure our index doesn't remove any of the 0's from the original vector
Soln = A(I1 ~= 0); %# Obtain solution using nonzero entries of the index