[R pcols]=rref(A);
A(:,pcols)=[];
You deleted the pivot columns out of A. Whatever is left must be non-pivot columns.
[r,fcols]=size(A);
fcols will be the number of columns in the portion of A that remains -- at this point, the number of non-pivot columns. fcols will be a scalar such as 6 if A were 4 x 6 at that point
npc = A(:,fcols);
A indexed with a scalar column index is going to return something that has exactly one column (provided that A is not empty... you would get an error if A were empty.)
But surely you want all of what remains of A, not just the last non-pivot column.
