Z is a 51 row X 3 column matrix. I need to obtain the 51 X 51 matrix H = Z(Z'Z)^(-1)Z', where ' denotes transpose and ^(-1) means inverse. H is idempotent, so as a check, either H'H or HH' should yield an identity matrix. Straightforward evaluation of H evidently yields an incorrect result, as H'H is not an identity matrix.. Can MathCad handle matrices this large? Or are there special procedures for dealing with such matrices?