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97 lines
3.8 KiB
Fortran
97 lines
3.8 KiB
Fortran
*DECK CG
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SUBROUTINE CG (NM, N, AR, AI, WR, WI, MATZ, ZR, ZI, FV1, FV2, FV3,
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+ IERR)
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C***BEGIN PROLOGUE CG
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C***PURPOSE Compute the eigenvalues and, optionally, the eigenvectors
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C of a complex general matrix.
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C***LIBRARY SLATEC (EISPACK)
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C***CATEGORY D4A4
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C***TYPE COMPLEX (RG-S, CG-C)
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C***KEYWORDS EIGENVALUES, EIGENVECTORS, EISPACK
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C***AUTHOR Smith, B. T., et al.
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C***DESCRIPTION
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C
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C This subroutine calls the recommended sequence of
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C subroutines from the eigensystem subroutine package (EISPACK)
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C to find the eigenvalues and eigenvectors (if desired)
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C of a COMPLEX GENERAL matrix.
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C
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C On INPUT
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C
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C NM must be set to the row dimension of the two-dimensional
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C array parameters, AR, AI, ZR and ZI, as declared in the
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C calling program dimension statement. NM is an INTEGER
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C variable.
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C
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C N is the order of the matrix A=(AR,AI). N is an INTEGER
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C variable. N must be less than or equal to NM.
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C
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C AR and AI contain the real and imaginary parts, respectively,
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C of the complex general matrix. AR and AI are two-dimensional
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C REAL arrays, dimensioned AR(NM,N) and AI(NM,N).
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C
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C MATZ is an INTEGER variable set equal to zero if only
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C eigenvalues are desired. Otherwise, it is set to any
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C non-zero integer for both eigenvalues and eigenvectors.
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C
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C On OUTPUT
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C
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C WR and WI contain the real and imaginary parts, respectively,
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C of the eigenvalues. WR and WI are one-dimensional REAL
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C arrays, dimensioned WR(N) and WI(N).
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C
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C ZR and ZI contain the real and imaginary parts, respectively,
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C of the eigenvectors if MATZ is not zero. ZR and ZI are
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C two-dimensional REAL arrays, dimensioned ZR(NM,N) and
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C ZI(NM,N).
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C
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C IERR is an INTEGER flag set to
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C Zero for normal return,
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C 10*N if N is greater than NM,
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C J if the J-th eigenvalue has not been
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C determined after a total of 30 iterations.
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C The eigenvalues should be correct for indices
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C IERR+1, IERR+2, ..., N, but no eigenvectors are
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C computed.
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C
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C FV1, FV2, and FV3 are one-dimensional REAL arrays used for
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C temporary storage, dimensioned FV1(N), FV2(N), and FV3(N).
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C
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C Questions and comments should be directed to B. S. Garbow,
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C APPLIED MATHEMATICS DIVISION, ARGONNE NATIONAL LABORATORY
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C ------------------------------------------------------------------
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C
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C***REFERENCES B. T. Smith, J. M. Boyle, J. J. Dongarra, B. S. Garbow,
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C Y. Ikebe, V. C. Klema and C. B. Moler, Matrix Eigen-
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C system Routines - EISPACK Guide, Springer-Verlag,
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C 1976.
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C***ROUTINES CALLED CBABK2, CBAL, COMQR, COMQR2, CORTH
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C***REVISION HISTORY (YYMMDD)
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C 760101 DATE WRITTEN
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C 890831 Modified array declarations. (WRB)
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C 890831 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 920501 Reformatted the REFERENCES section. (WRB)
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C***END PROLOGUE CG
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C
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INTEGER N,NM,IS1,IS2,IERR,MATZ
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REAL AR(NM,*),AI(NM,*),WR(*),WI(*),ZR(NM,*),ZI(NM,*)
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REAL FV1(*),FV2(*),FV3(*)
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C
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C***FIRST EXECUTABLE STATEMENT CG
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IF (N .LE. NM) GO TO 10
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IERR = 10 * N
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GO TO 50
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C
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10 CALL CBAL(NM,N,AR,AI,IS1,IS2,FV1)
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CALL CORTH(NM,N,IS1,IS2,AR,AI,FV2,FV3)
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IF (MATZ .NE. 0) GO TO 20
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C .......... FIND EIGENVALUES ONLY ..........
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CALL COMQR(NM,N,IS1,IS2,AR,AI,WR,WI,IERR)
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GO TO 50
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C .......... FIND BOTH EIGENVALUES AND EIGENVECTORS ..........
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20 CALL COMQR2(NM,N,IS1,IS2,FV2,FV3,AR,AI,WR,WI,ZR,ZI,IERR)
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IF (IERR .NE. 0) GO TO 50
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CALL CBABK2(NM,N,IS1,IS2,FV1,N,ZR,ZI)
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50 RETURN
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END
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