stev(3)

📦
version 3.12.1 · 9 versions
, in arch rolling

🌸 NAME 🌸

okay bestie, you're looking at stev(3) from the Library Functions Manual. The NAME line is exactly: stev - stev: eig, QR iteration. That's the whole name tea. 💅

✨ SYNOPSIS ✨

two subroutines, same argument-list vibe:

       subroutine dstev (jobz, n, d, e, z, ldz, work, info)
            DSTEV computes the eigenvalues and, optionally, the left and/or
           right eigenvectors for OTHER matrices
       subroutine sstev (jobz, n, d, e, z, ldz, work, info)
            SSTEV computes the eigenvalues and, optionally, the left and/or
           right eigenvectors for OTHER matrices

💖 Detailed Description 💖

No extra prose in the original here — it just rolls straight into Function Documentation. Keep scrolling, bestie. 🫶

🧚 Function Documentation 🧚

💅 subroutine dstev (character jobz, integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer info)

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

🎀 Purpose 🎀

DSTEV computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A.

🌸 Parameters 🌸

  • JOBZ — JOBZ is CHARACTER*1; = 'N': Compute eigenvalues only; = 'V': Compute eigenvalues and eigenvectors.
  • N — N is INTEGER; the order of the matrix. N >= 0.
  • D — D is DOUBLE PRECISION array, dimension (N). On entry, the n diagonal elements of the tridiagonal matrix A. On exit, if INFO = 0, the eigenvalues in ascending order.
  • E — E is DOUBLE PRECISION array, dimension (N-1). On entry, the (n-1) subdiagonal elements of the tridiagonal matrix A, stored in elements 1 to N-1 of E. On exit, the contents of E are destroyed.
💀 destruction alert, bestie: E does not survive the call.
  • 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 D(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(1,2*N-2)). If JOBZ = 'N', WORK is not referenced.
  • 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 E did not converge to zero.

👑 Author 👑

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

Definition at line 115 of file dstev.f.

🦋 subroutine sstev (character jobz, integer n, real, dimension( * ) d, real, dimension( * ) e, real, dimension( ldz, * ) z, integer ldz, real, dimension( * ) work, integer info)

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

🎀 Purpose 🎀

SSTEV computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A.

🌸 Parameters 🌸

  • JOBZ — JOBZ is CHARACTER*1; = 'N': Compute eigenvalues only; = 'V': Compute eigenvalues and eigenvectors.
  • N — N is INTEGER; the order of the matrix. N >= 0.
  • D — D is REAL array, dimension (N). On entry, the n diagonal elements of the tridiagonal matrix A. On exit, if INFO = 0, the eigenvalues in ascending order.
  • E — E is REAL array, dimension (N-1). On entry, the (n-1) subdiagonal elements of the tridiagonal matrix A, stored in elements 1 to N-1 of E. On exit, the contents of E are destroyed.
💀 again, E gets absolutely cooked. do not expect it back.
  • Z — Z is REAL 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 D(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 REAL array, dimension (max(1,2*N-2)). If JOBZ = 'N', WORK is not referenced.
  • 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 E did not converge to zero.

👑 Author 👑

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

Definition at line 115 of file sstev.f.

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

that's the whole page, bestie. shoutout to LAPACK, Version 3.12.0, and the stev(3) footer — there's no date in the footer, so I'm not inventing one. 💖

📦 where this page comes from