  backsub
  Builtin Function



      SSyynnooppssiiss
        Solution of Ax = B by backsubstitution.

      SSyynnttaaxx
        backsub ( _L_I_S_T, _B )

      DDeessccrriippttiioonn
        The backsub function computes the solution to the set of linear
        equations described by:


          A * X = B


     The 1st argument to backsub (_L_I_S_T) is the result from `factor(A)'.
     The second argument to backsub is the matrix _B.  _B can contain
     multiple right hand sides.

     Backsub returns a matrix _X which contains the solution(s) to the
     aforementioned equations.

     Backsub utilizes the LAPACK subroutines DGETRS or ZGETRS if _L_I_S_T
     contains LU factors or LAPACK subroutins DSYTRS or ZHETRS if _L_I_S_T
     contains the LDL factors.

     Example:


          > A = [1,2,3;4,5,6;7,8,0]
                  1          2          3
                  4          5          6
                  7          8          0
          > B = [1;2;3]
                  1
                  2
                  3
          > X = backsub(factor(A), B)
             -0.333
              0.667
          -3.52e-18
          > A*X - B
                  0
                  0
                  0





     SSeeee AAllssoo
        factor, inv, lu, solve










