SRC/dspgst.f(3)

okay so bestie, welcome to SRC/dspgst.f(3), straight out of the Library Functions Manual 💖 This is the DSPGST page, and it's giving packed-storage, real-symmetric-definite generalized eigenproblem energy. No cap, it's a whole vibe. 💅✨

💖 NAME 💖

SRC/dspgst.f

🌸 SYNOPSIS 🌸

Functions/Subroutines

subroutine dspgst (itype, uplo, n, ap, bp, info)
    DSPGST

🦋 Function/Subroutine Documentation 🦋

subroutine dspgst (integer itype, character uplo, integer n, double
precision, dimension( * ) ap, double precision, dimension( * ) bp,
integer info)

DSPGST

✨ Purpose ✨

okay so DSPGST reduces a real symmetric-definite generalized eigenproblem to standard form, using packed storage. Compact queen behavior, honestly. 🎀

If ITYPE = 1, the problem is A*x = lambda*B*x, and A is overwritten by inv(U**T)*A*inv(U) or inv(L)*A*inv(L**T).

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**T or L**T*A*L.

bestie, important: B must have been previously factorized as U**T*U or L*L**T by DPPTRF. That's not optional, fr fr. 💀

🎀 Parameters 🎀

ITYPE

ITYPE is INTEGER.

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

UPLO

UPLO is CHARACTER*1.

• = 'U': Upper triangle of A is stored and B is factored as U**T*U;
• = 'L': Lower triangle of A is stored and B is factored as L*L**T.

N

N is INTEGER. It's the order of the matrices A and B. N >= 0. periodt. 💅

AP

AP is DOUBLE PRECISION array, dimension (N*(N+1)/2).

On entry, it's the upper or lower triangle of the symmetric 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, it holds the transformed matrix, stored in the same format as A. iconic. ✨

BP

BP is DOUBLE PRECISION array, dimension (N*(N+1)/2).

It's the triangular factor from the Cholesky factorization of B, stored in the same format as A, as returned by DPPTRF. 🫶

INFO

INFO is INTEGER.

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

👑 Author 👑

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

Definition at line 112 of file dspgst.f.

💜 Author 💜

Generated automatically by Doxygen for LAPACK from the source code.

---

okay that's the whole page, bestie! 💖 This was LAPACK Version 3.12.0 realness from SRC/dspgst.f(3). Go forth and slay those packed symmetric-definite generalized eigenproblems! 💅✨🦋