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

NAME

cpttrs - solve a tridiagonal system of the form A * X = B using the factorization A = U'*D*U or A = L*D*L' computed by CPTTRF

SYNOPSIS

  SUBROUTINE CPTTRS( UPLO, N, NRHS, DIAG, OFFD, B, LDB, INFO)
  CHARACTER * 1 UPLO
  COMPLEX OFFD(*), B(LDB,*)
  INTEGER N, NRHS, LDB, INFO
  REAL DIAG(*)

  SUBROUTINE CPTTRS_64( UPLO, N, NRHS, DIAG, OFFD, B, LDB, INFO)
  CHARACTER * 1 UPLO
  COMPLEX OFFD(*), B(LDB,*)
  INTEGER*8 N, NRHS, LDB, INFO
  REAL DIAG(*)

F95 INTERFACE

  SUBROUTINE PTTRS( UPLO, [N], [NRHS], DIAG, OFFD, B, [LDB], [INFO])
  CHARACTER(LEN=1) :: UPLO
  COMPLEX, DIMENSION(:) :: OFFD
  COMPLEX, DIMENSION(:,:) :: B
  INTEGER :: N, NRHS, LDB, INFO
  REAL, DIMENSION(:) :: DIAG

  SUBROUTINE PTTRS_64( UPLO, [N], [NRHS], DIAG, OFFD, B, [LDB], [INFO])
  CHARACTER(LEN=1) :: UPLO
  COMPLEX, DIMENSION(:) :: OFFD
  COMPLEX, DIMENSION(:,:) :: B
  INTEGER(8) :: N, NRHS, LDB, INFO
  REAL, DIMENSION(:) :: DIAG

C INTERFACE

#include <sunperf.h>

void cpttrs(char uplo, int n, int nrhs, float *diag, complex *offd, complex *b, int ldb, int *info);

void cpttrs_64(char uplo, long n, long nrhs, float *diag, complex *offd, complex *b, long ldb, long *info);

PURPOSE

cpttrs solves a tridiagonal system of the form A * X = B using the factorization A = U'*D*U or A = L*D*L' computed by CPTTRF. D is a diagonal matrix specified in the vector D, U (or L) is a unit bidiagonal matrix whose superdiagonal (subdiagonal) is specified in the vector E, and X and B are N by NRHS matrices.

ARGUMENTS

• UPLO (input)
  Specifies the form of the factorization and whether the vector OFFD is the superdiagonal of the upper bidiagonal factor U or the subdiagonal of the lower bidiagonal factor L. = 'U': A = U'*DIAG*U, OFFD is the superdiagonal of U

   = 'L':  A  = L*DIAG*L', OFFD is the subdiagonal of L

• N (input)
  The order of the tridiagonal matrix A. N > = 0.

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

• DIAG (input)
  The n diagonal elements of the diagonal matrix DIAG from the factorization A = U'*DIAG*U or A = L*DIAG*L'.

• OFFD (input/output)
  If UPLO = 'U', the (n-1) superdiagonal elements of the unit bidiagonal factor U from the factorization A = U'*DIAG*U. If UPLO = 'L', the (n-1) subdiagonal elements of the unit bidiagonal factor L from the factorization A = L*DIAG*L'.

• B (input/output)
  On entry, the right hand side vectors B for the system of linear equations. On exit, 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  = -k, the k-th argument had an illegal value