.TH BSpar_sym_solve 3 "2/12/1996" " " "BlockSolve95"
.SH NAME
BSpar_sym_solve \- Solve a symmetric positive definite system of equations
using conjugate gradients preconditioned by one of several
preconditioners.  The rhs can be a block of vectors.  The
user should not call this function directly, but BSpar_solve().

.SH INPUT PARAMETERS
.PD 0
.TP
.B BS 
- the number of vectors in the RHS
.PD 1
.PD 0
.TP
.B A 
- a sparse matrix
.PD 1
.PD 0
.TP
.B fact_A 
- the incomplete factored version of A, if any
.PD 1
.PD 0
.TP
.B comm_A 
- the communication structure for A
.PD 1
.PD 0
.TP
.B in_rhs 
- the contiguous block of vectors forming the rhs
.PD 1
.PD 0
.TP
.B pre_option 
- the preconditioner to use
.PD 1
.br
       PRE_ICC: incomplete Cholesky factorization
.br
       PRE_ILU: incomplete LU factorization
.br
       PRE_SSOR: Successive over relaxation
.br
       PRE_BJACOBI: Block Jacobi
.PD 0
.TP
.B err_tol 
- the tolerance to which to solve the problem
stop if the estimated norm of the residual divided by
the norm of the rhs is less than err_tol
.PD 1
.PD 0
.TP
.B max_iter 
- the maximum number of iterations to take
.PD 1
.PD 0
.TP
.B residual 
- the final computed residual
.PD 1
.PD 0
.TP
.B guess 
- if TRUE, then initialize out_x to 0, otherwise the program
assumes that out_x contains an initial guess
.PD 1
.PD 0
.TP
.B procinfo 
- the usual processor stuff
.PD 1

.SH OUTPUT PARAMETERS
.PD 0
.TP
.B out_x 
- the contiguous block of vectors containing the solution
.PD 1

.SH RETURNS
The number of iterations or a negative number indicating the number
of iterations prior to finding that the matrix (or preconditioner)
is not positive definite.

.SH NOTES
The preconditioners must be computed prior to calling BSpar_isolve.
For more information on the preconditioners, see the manual.
.SH SYNOPSIS
.nf
int BSpar_sym_solve(int BS, BSpar_mat *A, BSpar_mat *fact_A, BScomm *comm_A,
 FLOAT *in_rhs, FLOAT *out_x, int pre_option, FLOAT err_tol, int max_iter,
 FLOAT *residual, int guess, BSprocinfo *procinfo)

.fi

.SH LOCATION
 BlockSolve95/src/BSpar_sym_solve.c