CGGBAK(3)

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🌸 NAME 🌸

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/cggbak.f

That's the whole name section, bestie — it's literally just the source file path 🫶

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✨ SYNOPSIS ✨

🎀 Functions/Subroutines 🎀

       subroutine CGGBAK (job, side, n, ilo, ihi, lscale, rscale, m, v, ldv,
           info)
           CGGBAK

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💖 Function/Subroutine Documentation 💖

   subroutine CGGBAK (character job, character side, integer n, integer ilo,
       integer ihi, real, dimension( * ) lscale, real, dimension( * ) rscale,
       integer m, complex, dimension( ldv, * ) v, integer ldv, integer info)
       CGGBAK

🦋 Purpose

okay so CGGBAK forms the right or left eigenvectors of a complex generalized eigenvalue problem A*x = lambda*B*x, by backward transformation on the computed eigenvectors of the balanced pair of matrices output by CGGBAL. That's the whole main-character job, no cap 💅

🌈 Parameters

• JOB — this one is CHARACTER*1, bestie. It specifies the type of backward transformation required:
  • = 'N': do nothing, return immediately;
  • = 'P': do backward transformation for permutation only;
  • = 'S': do backward transformation for scaling only;
  • = 'B': do backward transformations for both permutation and scaling.

JOB must be the same as the argument JOB supplied to CGGBAL. fr fr, match the vibes.

• SIDE — CHARACTER*1. It says which flavor of eigenvectors lives in V:
  • = 'R': V contains right eigenvectors;
  • = 'L': V contains left eigenvectors.
• N — INTEGER. The number of rows of the matrix V. N >= 0.
• ILO — INTEGER.
• IHI — INTEGER. The integers ILO and IHI determined by CGGBAL. 1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
• LSCALE — REAL array, dimension (N). Details of the permutations and/or scaling factors applied to the left side of A and B, as returned by CGGBAL.
• RSCALE — REAL array, dimension (N). Details of the permutations and/or scaling factors applied to the right side of A and B, as returned by CGGBAL.
• M — INTEGER. The number of columns of the matrix V. M >= 0.
• V — COMPLEX array, dimension (LDV,M). On entry, the matrix of right or left eigenvectors to be transformed, as returned by CTGEVC. On exit, V is overwritten by the transformed eigenvectors. iconic behavior, honestly 🔥
• LDV — INTEGER. The leading dimension of the matrix V. LDV >= max(1,N).
• INFO — INTEGER.
  • = 0: successful exit.
  • < 0: if INFO = -i, the i-th argument had an illegal value.

👑 Author

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

🧚 Further Details

See R.C. Ward, Balancing the generalized eigenvalue problem, SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.

Definition at line 146 of file cggbak.f.

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⭐ Author ⭐

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