SRC/sstev.f(3)

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🎀 NAME 🎀

SRC/sstev.f — yes, that's the name. Short, iconic, to the point. 🫶

✨ SYNOPSIS ✨

🫶 Functions/Subroutines

• 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

🦋 Function/Subroutine Documentation 🦋

Here's the full signature, character for character:

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. 💀 fr fr, they're gone.

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.

Definition at line 115 of file sstev.f.

🌈 Author

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