SRC/dspev.f(3)

SRC/dspev.f(3) — Library Functions Manual vibes 💖

Hey bestie! 💖 This is the page for SRC/dspev.f(3) from the Library Functions Manual. It’s LAPACK, it’s Fortran, it’s giving main-character linear algebra. Let’s get into it. ✨

📛 NAME

SRC/dspev.f

That’s the name, no cap. 💅

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✨ SYNOPSIS

Functions/Subroutines

       subroutine dspev (jobz, uplo, n, ap, w, z, ldz, work, info)

DSPEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices — yes, “OTHER” is loud on purpose. 🔥

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💅 Function/Subroutine Documentation

   subroutine dspev (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 info)

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

🎯 Purpose

Okay so the purpose is literally this: DSPEV computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage. Slay. ✨

🧮 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 (3*N).
• 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 129 of file dspev.f.

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🧚 Author

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💖 That’s the whole vibe, bestie! 💖 Footer sign-off: LAPACK Version 3.12.0, SRC/dspev.f(3). No separate date is printed on the footer — just version/file energy. Now go pack a symmetric matrix and slay. 💅✨