SRC/dspevd.f(3)

💖 SRC/dspevd.f(3) 💖

okay so welcome to the Library Functions Manual page for SRC/dspevd.f — yes, the (3) page, the LAPACK bestie, the one and only. No cap, this routine is about packed symmetric matrix eigenvalues and it is lowkey iconic. 🎀

---

✨ NAME ✨

SRC/dspevd.f

🌸 SYNOPSIS 🌸

🫶 Functions/Subroutines

subroutine dspevd

subroutine dspevd (jobz, uplo, n, ap, w, z, ldz, work, lwork, iwork,
    liwork, info)

DSPEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

🦋 Function/Subroutine Documentation 🦋

💅 subroutine dspevd

subroutine dspevd (character jobz, character uplo, integer n, double
    precision, dimension( * ) ap, double precision, dimension( * ) w, double
    precision, dimension( ldz, * ) z, integer ldz, double precision,
    dimension( * ) work, integer lwork, integer, dimension( * ) iwork,
    integer liwork, integer info)

DSPEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices. That's the whole assignment, bestie. 🫶

✨ Purpose ✨

DSPEVD computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage. If eigenvectors are desired, it uses a divide and conquer algorithm. Literally the plot of the whole function. 💜

🎀 Parameters 🎀

JOBZ

JOBZ is CHARACTER*1

• = 'N': Compute eigenvalues only;
• = 'V': Compute eigenvalues and eigenvectors.

UPLO

UPLO is CHARACTER*1

• = 'U': Upper triangle of A is stored;
• = 'L': Lower triangle of A is stored.

N

N is INTEGER

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

AP

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

On entry, 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)*(2*n-j)/2) = A(i,j) for j<=i<=n.

On exit, AP is overwritten by values generated during the reduction to tridiagonal form. If UPLO = 'U', the diagonal and first superdiagonal of the tridiagonal matrix T overwrite the corresponding elements of A, and if UPLO = 'L', the diagonal and first subdiagonal of T overwrite the corresponding elements of A.

W

W is DOUBLE PRECISION array, dimension (N)

If INFO = 0, the eigenvalues in ascending order.

Z

Z is DOUBLE PRECISION array, dimension (LDZ, N)

If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal eigenvectors of the matrix A, with the i-th column of Z holding the eigenvector associated with W(i).

If JOBZ = 'N', then Z is not referenced.

LDZ

LDZ is INTEGER

The leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= max(1,N).

WORK

WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))

On exit, if INFO = 0, WORK(1) returns the required LWORK.

LWORK

LWORK is INTEGER

The dimension of the array WORK.

• If N <= 1, LWORK must be at least 1.
• If JOBZ = 'N' and N > 1, LWORK must be at least 2*N.
• If JOBZ = 'V' and N > 1, LWORK must be at least 1 + 6*N + N**2.

If LWORK = -1, then a workspace query is assumed; the routine only calculates the required sizes of the WORK and IWORK arrays, returns these values as the first entries of the WORK and IWORK arrays, and no error message related to LWORK or LIWORK is issued by XERBLA.

IWORK

IWORK is INTEGER array, dimension (MAX(1,LIWORK))

On exit, if INFO = 0, IWORK(1) returns the required LIWORK.

LIWORK

LIWORK is INTEGER

The dimension of the array IWORK.

• If JOBZ = 'N' or N <= 1, LIWORK must be at least 1.
• If JOBZ = 'V' and N > 1, LIWORK must be at least 3 + 5*N.

If LIWORK = -1, then a workspace query is assumed; the routine only calculates the required sizes of the WORK and IWORK arrays, returns these values as the first entries of the WORK and IWORK arrays, and no error message related to LWORK or LIWORK is issued by XERBLA.

INFO

INFO is INTEGER

• = 0: successful exit
• < 0: if INFO = -i, the i-th argument had an illegal value.
• > 0: if INFO = i, the algorithm failed to converge; i off-diagonal elements of an intermediate tridiagonal form did not converge to zero.

👑 Author 👑

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

📍 Definition at line 170 of file dspevd.f. 📍

Definition at line 170 of file dspevd.f.

🤖 Author (Doxygen edition) 🤖

Generated automatically by Doxygen for LAPACK from the source code.

---

okay that's the whole page, bestie. Footer vibe check: this is from LAPACK Version 3.12.0, page SRC/dspevd.f(3) — and the footer has no extra date line, so that's the whole source/version situation. Slay, you made it to the end. 💖✨🎀