SRC/csteqr.f(3)

💖 NAME 💖

SRC/csteqr.f — bestie, this is the CSTEQR page from the Library Functions Manual, and yes the manual name is folded in right here instead of copying the header line. iconic behavior, tbh ✨

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🦋 SYNOPSIS 🦋

✨ Functions/Subroutines ✨

       subroutine csteqr (compz, n, d, e, z, ldz, work, info)
           CSTEQR

🌸 Function/Subroutine Documentation 🌸

✨ CSTEQR ✨

   subroutine csteqr (character compz, integer n, real, dimension( * ) d, real,
       dimension( * ) e, complex, dimension( ldz, * ) z, integer ldz, real,
       dimension( * ) work, integer info)

💅 Purpose 💅

okay so CSTEQR computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. The eigenvectors of a full or band complex Hermitian matrix can also be found if CHETRD or CHPTRD or CHBTRD has been used to reduce this matrix to tridiagonal form. That's the assignment, and it literally ate 💅

🎀 Parameters 🎀

• COMPZ — COMPZ is CHARACTER*1. The values are:
  • = 'N': compute eigenvalues only.
  • = 'V': compute eigenvalues and eigenvectors of the original Hermitian matrix. On entry, Z must contain the unitary matrix used to reduce the original matrix to tridiagonal form.
  • = 'I': compute eigenvalues and eigenvectors of the tridiagonal matrix. Z is initialized to the identity matrix.
• N — N is INTEGER. The order of the matrix. N >= 0.
• D — D is REAL array, dimension (N). On entry, the diagonal elements of the tridiagonal matrix. 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. On exit, E has been destroyed. RIP E, ngl 🫡
• Z — Z is COMPLEX array, dimension (LDZ, N). On entry, if COMPZ = 'V', then Z contains the unitary matrix used in the reduction to tridiagonal form. On exit, if INFO = 0, then if COMPZ = 'V', Z contains the orthonormal eigenvectors of the original Hermitian matrix, and if COMPZ = 'I', Z contains the orthonormal eigenvectors of the symmetric tridiagonal matrix. If COMPZ = 'N', then Z is not referenced.
• LDZ — LDZ is INTEGER. The leading dimension of the array Z. LDZ >= 1, and if eigenvectors are desired, then LDZ >= max(1,N).
• WORK — WORK is REAL array, dimension (max(1,2*N-2)). If COMPZ = 'N', then WORK is not referenced.
• INFO — INFO is INTEGER. The exit-status lore is:
  • = 0: successful exit
  • < 0: if INFO = -i, the i-th argument had an illegal value
  • > 0: the algorithm has failed to find all the eigenvalues in a total of 30*N iterations; if INFO = i, then i elements of E have not converged to zero; on exit, D and E contain the elements of a symmetric tridiagonal matrix which is unitarily similar to the original matrix.

🌈 Author 🌈

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

Definition at line 131 of file csteqr.f.

👑 Author 👑

Generated automatically by Doxygen for LAPACK from the source code. not me being auto-generated by Doxygen for LAPACK from the source code 💀✨

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okay bye bestie 💖 this footer moment is LAPACK Version 3.12.0 on page SRC/csteqr.f(3) — mwah! 🫶✨