

   SSoollvvee aann UUppppeerr TTrriiaanngguullaarr SSyysstteemm

        backsolve(r, x, k=ncol(r))

   AArrgguummeennttss::

          r: an upper triangular matrix giving the coefficients
             for the system to be solved.  Values below the
             diagonal are ignored.

          x: a matrix whose columns give ``right-hand sides''
             for the equations.

          k: The number or columns of `r' and rows of `x' to
             use.

   VVaalluuee::

        The solution of the triangular system.  The result will
        be a a vector if `x' is a vector and a matrix if `x' is
        a matrix.

   RReeffeerreenncceess::

        Dongarra, J. J., J. R. Bunch, C. B. Moler and G. W.
        Stewart (1978).  LINPACK Users Guide.  Philadelphia:
        SIAM Publications.

   SSeeee AAllssoo::

        `chol', `qr', `solve'.

   EExxaammpplleess::

        # no examples yet

