---
name: "cgtsv"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/cgtsv/3lapack"
---

# cgtsv(3lapack)

solves the equation A\*X = B,

## NAME

CGTSV - solves the equation   A\*X = B,

## SYNOPSIS

- SUBROUTINE CGTSV(

  N, NRHS, DL, D, DU, B, LDB, INFO )

- INTEGER

  INFO, LDB, N, NRHS

- COMPLEX

  B( LDB, \* ), D( \* ), DL( \* ), DU( \* )

## 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) INTEGER

  The order of the matrix A.  N \>= 0.

- NRHS (input) INTEGER

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

- DL (input/output) COMPLEX array, dimension (N-1)

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

- D (input/output) COMPLEX array, dimension (N)

  On entry, D must contain the diagonal elements of A. On exit, D is overwritten by the n diagonal elements of U.

- DU (input/output) COMPLEX array, dimension (N-1)

  On entry, DU must contain the (n-1) superdiagonal elements of A. On exit, DU is overwritten by the (n-1) elements of the first superdiagonal of U.

- B (input/output) COMPLEX array, dimension (LDB,NRHS)

  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) INTEGER

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

- INFO (output) INTEGER

  \= 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.