---
name: "cptts2"
section: "3lapack"
platform: "linux"
package: "liblapack-doc"
version: "3.2.1-8"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/cptts2/3lapack"
---

# cptts2(3lapack)

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

## NAME

CPTTS2 - 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

## SYNOPSIS

- SUBROUTINE CPTTS2(

  IUPLO, N, NRHS, D, E, B, LDB )

- INTEGER

  IUPLO, LDB, N, NRHS

- REAL

  D( \* )

- COMPLEX

  B( LDB, \* ), E( \* )

## PURPOSE

CPTTS2 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

- IUPLO (input) INTEGER

  Specifies the form of the factorization and whether the vector E is the superdiagonal of the upper bidiagonal factor U or the subdiagonal of the lower bidiagonal factor L. = 1:  A = U'\*D\*U, E is the superdiagonal of U\
   \= 0:  A = L\*D\*L', E is the subdiagonal of L

- N (input) INTEGER

  The order of the tridiagonal 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.

- D (input) REAL array, dimension (N)

  The n diagonal elements of the diagonal matrix D from the factorization A = U'\*D\*U or A = L\*D\*L'.

- E (input) COMPLEX array, dimension (N-1)

  If IUPLO = 1, the (n-1) superdiagonal elements of the unit bidiagonal factor U from the factorization A = U'\*D\*U. If IUPLO = 0, the (n-1) subdiagonal elements of the unit bidiagonal factor L from the factorization A = L\*D\*L'.

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

  On entry, the right hand side vectors B for the system of linear equations. On exit, the solution vectors, X.

- LDB (input) INTEGER

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