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

NAME

cgtsv - solve the equation A*X = B,

SYNOPSIS

  SUBROUTINE CGTSV( N, NRHS, LOW, DIAG, UP, B, LDB, INFO)
  COMPLEX LOW(*), DIAG(*), UP(*), B(LDB,*)
  INTEGER N, NRHS, LDB, INFO

  SUBROUTINE CGTSV_64( N, NRHS, LOW, DIAG, UP, B, LDB, INFO)
  COMPLEX LOW(*), DIAG(*), UP(*), B(LDB,*)
  INTEGER*8 N, NRHS, LDB, INFO

F95 INTERFACE

  SUBROUTINE GTSV( [N], [NRHS], LOW, DIAG, UP, B, [LDB], [INFO])
  COMPLEX, DIMENSION(:) :: LOW, DIAG, UP
  COMPLEX, DIMENSION(:,:) :: B
  INTEGER :: N, NRHS, LDB, INFO

  SUBROUTINE GTSV_64( [N], [NRHS], LOW, DIAG, UP, B, [LDB], [INFO])
  COMPLEX, DIMENSION(:) :: LOW, DIAG, UP
  COMPLEX, DIMENSION(:,:) :: B
  INTEGER(8) :: N, NRHS, LDB, INFO

C INTERFACE

#include <sunperf.h>

void cgtsv(int n, int nrhs, complex *low, complex *diag, complex *up, complex *b, int ldb, int *info);

void cgtsv_64(long n, long nrhs, complex *low, complex *diag, complex *up, complex *b, long ldb, long *info);

PURPOSE

cgtsv solves the equation

where A is an N-by-N tridiagonal matrix, by Gaussian elimination with partial pivoting.

Note that the equation A'*X = B may be solved by interchanging the order of the arguments DU and DL.

ARGUMENTS

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

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

• LOW (input/output)
  On entry, LOW must contain the (n-1) subdiagonal elements of A. On exit, LOW is overwritten by the (n-2) elements of the second superdiagonal of the upper triangular matrix U from the LU factorization of A, in LOW(1), ..., LOW(n-2).

• DIAG (input/output)
  On entry, DIAG must contain the diagonal elements of A. On exit, DIAG is overwritten by the n diagonal elements of U.

• UP (input/output)
  On entry, UP must contain the (n-1) superdiagonal elements of A. On exit, UP is overwritten by the (n-1) elements of the first superdiagonal of U.

• B (input/output)
  On entry, the N-by-NRHS right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS solution matrix 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 illegal value

   > 0:  if INFO  = i, U(i,i) is exactly zero, and the solution
  has not been computed.  The factorization has not been
  completed unless i  = N.