Contents

• NAME
• SYNOPSIS
  • F95 INTERFACE
  • C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

     sgttrs - solve one of the systems of equations  A*X =  B  or
     A'*X = B,

SYNOPSIS

     SUBROUTINE SGTTRS(TRANSA, N, NRHS, LOW, DIAG, UP1, UP2, IPIVOT, B,
           LDB, INFO)

     CHARACTER * 1 TRANSA
     INTEGER N, NRHS, LDB, INFO
     INTEGER IPIVOT(*)
     REAL LOW(*), DIAG(*), UP1(*), UP2(*), B(LDB,*)

     SUBROUTINE SGTTRS_64(TRANSA, N, NRHS, LOW, DIAG, UP1, UP2, IPIVOT, B,
           LDB, INFO)

     CHARACTER * 1 TRANSA
     INTEGER*8 N, NRHS, LDB, INFO
     INTEGER*8 IPIVOT(*)
     REAL LOW(*), DIAG(*), UP1(*), UP2(*), B(LDB,*)

  F95 INTERFACE
     SUBROUTINE GTTRS([TRANSA], [N], [NRHS], LOW, DIAG, UP1, UP2, IPIVOT,
            B, [LDB], [INFO])

     CHARACTER(LEN=1) :: TRANSA
     INTEGER :: N, NRHS, LDB, INFO
     INTEGER, DIMENSION(:) :: IPIVOT
     REAL, DIMENSION(:) :: LOW, DIAG, UP1, UP2
     REAL, DIMENSION(:,:) :: B

     SUBROUTINE GTTRS_64([TRANSA], [N], [NRHS], LOW, DIAG, UP1, UP2,
            IPIVOT, B, [LDB], [INFO])

     CHARACTER(LEN=1) :: TRANSA
     INTEGER(8) :: N, NRHS, LDB, INFO
     INTEGER(8), DIMENSION(:) :: IPIVOT
     REAL, DIMENSION(:) :: LOW, DIAG, UP1, UP2
     REAL, DIMENSION(:,:) :: B

  C INTERFACE
     #include <sunperf.h>

     void sgttrs(char transa, int n, int nrhs, float *low,  float
               *diag,  float *up1, float *up2, int *ipivot, float
               *b, int ldb, int *info);
     void sgttrs_64(char transa, long n, long nrhs,  float  *low,
               float *diag, float *up1, float *up2, long *ipivot,
               float *b, long ldb, long *info);

PURPOSE

     sgttrs solves one of the systems of equations
        A*X = B  or  A'*X = B, with a tridiagonal matrix A  using
     the LU factorization computed by SGTTRF.

ARGUMENTS

     TRANSA (input)
               Specifies the form of the system of equations.   =
               'N':  A * X = B  (No transpose)
               = 'T':  A'* X = B  (Transpose)
               = 'C':  A'* X = B  (Conjugate  transpose  =  Tran-
               spose)

               TRANSA is defaulted to 'N' for F95 INTERFACE.

     N (input) The order of the matrix A.

     NRHS (input)
               The number of right hand sides, i.e.,  the  number
               of columns of the matrix B.  NRHS >= 0.

     LOW (input)
               The (n-1) multipliers that  define  the  matrix  L
               from the LU factorization of A.

     DIAG (input)
               The n diagonal elements of  the  upper  triangular
               matrix U from the LU factorization of A.

     UP1 (input)
               The (n-1) elements of the first super-diagonal  of
               U.

     UP2 (input)
               The (n-2) elements of the second super-diagonal of
               U.

     IPIVOT (input)
               The pivot indices; for 1 <= i <= n, row i  of  the
               matrix   was   interchanged  with  row  IPIVOT(i).
               IPIVOT(i)  will  always  be  either  i   or   i+1;
               IPIVOT(i)  = i indicates a row interchange was not
               required.

     B (input/output)
               On entry, the matrix of right hand side vectors B.
               On  exit, B is overwritten by the solution vectors
               X.

     LDB (input)
               The leading dimension of  the  array  B.   LDB  >=
               max(1,N).

     INFO (output)
               = 0:  successful exit
               < 0:  if INFO = -i, the i-th argument had an ille-
               gal value