SRC/ssbev.f(3)

💖 NAME 💖

okay bestie, welcome to SRC/ssbev.f(3) — it's a Library Functions Manual page, and the page is literally named SRC/ssbev.f. No cap, that's the name. 💅

✨ SYNOPSIS ✨

🦋 Functions/Subroutines 🦋

• subroutine ssbev (jobz, uplo, n, kd, ab, ldab, w, z, ldz, work, info) — SSBEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices. iconic behavior ✨

🌸 Function/Subroutine Documentation 🌸

   subroutine ssbev (character jobz, character uplo, integer n, integer kd,
       real, dimension( ldab, * ) ab, integer ldab, real, dimension( * ) w,
       real, dimension( ldz, * ) z, integer ldz, real, dimension( * ) work,
       integer info)

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

🎀 Purpose 🎀

SSBEV computes all the eigenvalues and, optionally, eigenvectors of a real symmetric band matrix A. That's the whole purpose, and it ate. 💖

💅 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.

KD

• KD is INTEGER.
• The number of superdiagonals of the matrix A if UPLO = 'U', or the number of subdiagonals if UPLO = 'L'. KD >= 0.

AB

• AB is REAL array, dimension (LDAB, N).
• On entry, the upper or lower triangle of the symmetric band matrix A, stored in the first KD+1 rows of the array. The j-th column of A is stored in the j-th column of the array AB as follows:

if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).

• On exit, AB is overwritten by values generated during the reduction to tridiagonal form. If UPLO = 'U', the first superdiagonal and the diagonal of the tridiagonal matrix T are returned in rows KD and KD+1 of AB, and if UPLO = 'L', the diagonal and first subdiagonal of T are returned in the first two rows of AB.

LDAB

• LDAB is INTEGER.
• The leading dimension of the array AB. LDAB >= KD + 1.

W

• W is REAL array, dimension (N).
• If INFO = 0, the eigenvalues in ascending order.

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 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 REAL array, dimension (max(1,3*N-2)).

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 144 of file ssbev.f.

📚 Author 📚

Generated automatically by Doxygen for LAPACK from the source code.

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