SRC/DEPRECATED/cgegv.f(3)

💅 NAME

Manual page for SRC/DEPRECATED/cgegv.f — a.k.a. SRC/DEPRECATED/cgegv.f(3) in the LAPACK library manual, bestie. Yes, she's deprecated, but she still has lore. 🫶

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✨ SYNOPSIS

🌸 Functions/Subroutines

subroutine cgegv (jobvl, jobvr, n, a, lda, b, ldb, alpha, beta, vl,
     ldvl, vr, ldvr, work, lwork, rwork, info)

CGEGV computes the eigenvalues and, optionally, the left and/or right eigenvectors of a complex matrix pair (A,B).

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🌸 Function/Subroutine Documentation 🌸

subroutine cgegv (character jobvl, character jobvr, integer n, complex,
       dimension( lda, * ) a, integer lda, complex, dimension( ldb, * ) b,
       integer ldb, complex, dimension( * ) alpha, complex, dimension( * )
       beta, complex, dimension( ldvl, * ) vl, integer ldvl, complex,
       dimension( ldvr, * ) vr, integer ldvr, complex, dimension( * ) work,
       integer lwork, real, dimension( * ) rwork, integer info)

CGEGV computes the eigenvalues and, optionally, the left and/or right eigenvectors of a complex matrix pair (A,B).

🎀 Purpose

🚨 This routine is deprecated and has been replaced by routine CGGEV. Ma'am is retired but still on the books, no cap.

CGEGV computes the eigenvalues and, optionally, the left and/or right eigenvectors of a complex matrix pair (A,B).

Given two square matrices A and B, the generalized nonsymmetric eigenvalue problem (GNEP) is to find the eigenvalues lambda and corresponding (non-zero) eigenvectors x such that

A*x = lambda*B*x.

An alternate form is to find the eigenvalues mu and corresponding eigenvectors y such that

mu*A*y = B*y.

These two forms are equivalent with mu = 1/lambda and x = y if neither lambda nor mu is zero. In order to deal with the case that lambda or mu is zero or small, two values alpha and beta are returned for each eigenvalue, such that lambda = alpha/beta and mu = beta/alpha.

The vectors x and y in the above equations are right eigenvectors of the matrix pair (A,B). Vectors u and v satisfying

u**H*A = lambda*u**H*B  or  mu*v**H*A = v**H*B

are left eigenvectors of (A,B).

🫠 The source literally says: Note: this routine performs on A and B — yes, the blank spot is in the original. I am not inventing lore, bestie. 😭

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💖 Parameters

• JOBVL — CHARACTER*1
  • = 'N': do not compute the left generalized eigenvectors;
  • = 'V': compute the left generalized eigenvectors (returned in VL).
• JOBVR — CHARACTER*1
  • = 'N': do not compute the right generalized eigenvectors;
  • = 'V': compute the right generalized eigenvectors (returned in VR).
• N — INTEGER
  • The order of the matrices A, B, VL, and VR.
  • N >= 0.
• A — COMPLEX array, dimension (LDA, N)
  • On entry, the matrix A.
  • If JOBVL = 'V' or JOBVR = 'V', then on exit A contains the Schur form of A from the generalized Schur factorization of the pair (A,B) after balancing. If no eigenvectors were computed, then only the diagonal elements of the Schur form will be correct. See CGGHRD and CHGEQZ for details.
• LDA — INTEGER
  • The leading dimension of A.
  • LDA >= max(1,N).
• B — COMPLEX array, dimension (LDB, N)
  • On entry, the matrix B.
  • If JOBVL = 'V' or JOBVR = 'V', then on exit B contains the upper triangular matrix obtained from B in the generalized Schur factorization of the pair (A,B) after balancing. If no eigenvectors were computed, then only the diagonal elements of B will be correct. See CGGHRD and CHGEQZ for details.
• LDB — INTEGER
  • The leading dimension of B.
  • LDB >= max(1,N).
• ALPHA — COMPLEX array, dimension (N)
  • The complex scalars alpha that define the eigenvalues of GNEP.
• BETA — COMPLEX array, dimension (N)
  • The complex scalars beta that define the eigenvalues of GNEP.
  • Together, the quantities alpha = ALPHA(j) and beta = BETA(j) represent the j-th eigenvalue of the matrix pair (A,B), in one of the forms lambda = alpha/beta or mu = beta/alpha. Since either lambda or mu may overflow, they should not, in general, be computed.
• VL — COMPLEX array, dimension (LDVL,N)
  • If JOBVL = 'V', the left eigenvectors u(j) are stored in the columns of VL, in the same order as their eigenvalues.
  • Each eigenvector is scaled so that its largest component has abs(real part) + abs(imag. part) = 1, except for eigenvectors corresponding to an eigenvalue with alpha = beta = 0, which are set to zero.
  • Not referenced if JOBVL = 'N'.
• LDVL — INTEGER
  • The leading dimension of the matrix VL.
  • LDVL >= 1, and if JOBVL = 'V', LDVL >= N.
• VR — COMPLEX array, dimension (LDVR,N)
  • If JOBVR = 'V', the right eigenvectors x(j) are stored in the columns of VR, in the same order as their eigenvalues.
  • Each eigenvector is scaled so that its largest component has abs(real part) + abs(imag. part) = 1, except for eigenvectors corresponding to an eigenvalue with alpha = beta = 0, which are set to zero.
  • Not referenced if JOBVR = 'N'.
• LDVR — INTEGER
  • The leading dimension of the matrix VR.
  • LDVR >= 1, and if JOBVR = 'V', LDVR >= N.
• WORK — COMPLEX array, dimension (MAX(1,LWORK))
  • On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
• LWORK — INTEGER
  • The dimension of the array WORK.
  • LWORK >= max(1,2*N).
  • For good performance, LWORK must generally be larger.
  • To compute the optimal value of LWORK, call ILAENV to get blocksizes (for CGEQRF, CUNMQR, and CUNGQR.) Then compute:
    • NB — MAX of the blocksizes for CGEQRF, CUNMQR, and CUNGQR;
    • The optimal LWORK is MAX( 2*N, N*(NB+1) ).
  • If LWORK = -1, then a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this value as the first entry of the WORK array, and no error message related to LWORK is issued by XERBLA.
• RWORK — REAL array, dimension (8*N)
• INFO — INTEGER
  • = 0: successful exit
  • < 0: if INFO = -i, the i-th argument had an illegal value.
  • =1,...,N: The QZ iteration failed. No eigenvectors have been calculated, but ALPHA(j) and BETA(j) should be correct for j=INFO+1,...,N.
  • > N: errors that usually indicate LAPACK problems:
    • =N+1: error return from CGGBAL
    • =N+2: error return from CGEQRF
    • =N+3: error return from CUNMQR
    • =N+4: error return from CUNGQR
    • =N+5: error return from CGGHRD
    • =N+6: error return from CHGEQZ (other than failed iteration)
    • =N+7: error return from CTGEVC
    • =N+8: error return from CGGBAK (computing VL)
    • =N+9: error return from CGGBAK (computing VR)
    • =N+10: error return from CLASCL (various calls)

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👑 Author

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

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🦋 Further Details

Balancing

This driver calls CGGBAL to both permute and scale rows and columns of A and B. The permutations PL and PR are chosen so that PL*A*PR and PL*B*R will be upper triangular except for the diagonal blocks A(i:j,i:j) and B(i:j,i:j), with i and j as close together as possible. The diagonal scaling matrices DL and DR are chosen so that the pair DL*PL*A*PR*DR, DL*PL*B*PR*DR have elements close to one (except for the elements that start out zero.)

After the eigenvalues and eigenvectors of the balanced matrices have been computed, CGGBAK transforms the eigenvectors back to what they would have been (in perfect arithmetic) if they had not been balanced.

Contents of A and B on Exit

If any eigenvectors are computed (either JOBVL='V' or JOBVR='V' or both), then on exit the arrays A and B will contain the complex Schur form[*] of the versions of A and B. If no eigenvectors are computed, then only the diagonal blocks will be correct.

[*] In other words, upper triangular form.

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Definition at line 280 of file cgegv.f.

👑 Author

Generated automatically by Doxygen for LAPACK from the source code.

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💖 Signed, sealed, and lowkey slaying: LAPACK Version 3.12.0, straight from SRC/DEPRECATED/cgegv.f(3). Version and source noted, bestie — periodt. 🫶✨