Gauß -Jordan row reduction.

Summary of the instructions:

• rref: row reduction to echelon form. At level 2, the list of pivoting coefficients is given, this is useful to treat particular cases.
• RANG: like rref but creates 0 only under the diagonal.
• det and RDET: determinant (using respectively the O(n*n!) algorithm or row reduction)
• INVL: inverse of a matrix using row reduction
• LU2: given a square matrix, returns L^-1 and U s.t. A=LU (i.e. A=stk2 $^{-1}\times$stk1) where L and U are lower and upper triangular (maybe w.r.t. to a permutation matrix, this means that computing the inverse of L or U is trivial). For comparison, the built-in LU returns three matrices L, U and P s.t. A=PLU.
• SYST and SOLGEN: solution of a linear system.

Note that all instructions using row reduction show intermediate steps if flag 1 is set (1 SF). If flag 1 is cleared (1 CF), you get directly the results.