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

# chpgst(3lapack)

reduces a complex Hermitian-definite generalized eigenproblem to standard form, using packed storage

## NAME

CHPGST - reduces a complex Hermitian-definite generalized eigenproblem to standard form, using packed storage

## SYNOPSIS

- SUBROUTINE CHPGST(

  ITYPE, UPLO, N, AP, BP, INFO )

- CHARACTER

  UPLO

- INTEGER

  INFO, ITYPE, N

- COMPLEX

  AP( \* ), BP( \* )

## PURPOSE

CHPGST reduces a complex Hermitian-definite generalized eigenproblem to standard form, using packed storage. If ITYPE = 1, the problem is A\*x = lambda\*B\*x,\
 and A is overwritten by inv(U\*\*H)\*A\*inv(U) or inv(L)\*A\*inv(L\*\*H) If ITYPE = 2 or 3, the problem is A\*B\*x = lambda\*x or\
 B\*A\*x = lambda\*x, and A is overwritten by U\*A\*U\*\*H or L\*\*H\*A\*L. B must have been previously factorized as U\*\*H\*U or L\*L\*\*H by CPPTRF.

## ARGUMENTS

- ITYPE (input) INTEGER

  \= 1: compute inv(U\*\*H)\*A\*inv(U) or inv(L)\*A\*inv(L\*\*H);\
   \= 2 or 3: compute U\*A\*U\*\*H or L\*\*H\*A\*L.

- UPLO (input) CHARACTER\*1

  \= 'U':  Upper triangle of A is stored and B is factored as U\*\*H\*U; = 'L':  Lower triangle of A is stored and B is factored as L\*L\*\*H.

- N (input) INTEGER

  The order of the matrices A and B.  N \>= 0.

- AP (input/output) COMPLEX array, dimension (N\*(N+1)/2)

  On entry, the upper or lower triangle of the Hermitian matrix A, packed columnwise in a linear array.  The j-th column of A is stored in the array AP as follows: if UPLO = 'U', AP(i + (j-1)\*j/2) = A(i,j) for 1\<=i\<=j; if UPLO = 'L', AP(i + (j-1)\*(2n-j)/2) = A(i,j) for j\<=i\<=n. On exit, if INFO = 0, the transformed matrix, stored in the same format as A.

- BP (input) COMPLEX array, dimension (N\*(N+1)/2)

  The triangular factor from the Cholesky factorization of B, stored in the same format as A, as returned by CPPTRF.

- INFO (output) INTEGER

  \= 0:  successful exit\
   \< 0:  if INFO = -i, the i-th argument had an illegal value