ssiev.f
SUBROUTINE SSIEV (A, LDA, N, E, WORK, JOB, INFO)
C***BEGIN PROLOGUE SSIEV
C***PURPOSE Compute the eigenvalues and, optionally, the eigenvectors
C of a real symmetric matrix.
C***LIBRARY SLATEC
C***CATEGORY D4A1
C***TYPE SINGLE PRECISION (SSIEV-S, CHIEV-C)
C***KEYWORDS COMPLEX HERMITIAN, EIGENVALUES, EIGENVECTORS, MATRIX,
C SYMMETRIC
C***AUTHOR Kahaner, D. K., (NBS)
C Moler, C. B., (U. of New Mexico)
C Stewart, G. W., (U. of Maryland)
C***DESCRIPTION
C
C Abstract
C SSIEV computes the eigenvalues and, optionally, the eigenvectors
C of a real symmetric matrix.
C
C Call Sequence Parameters-
C (The values of parameters marked with * (star) will be changed
C by SSIEV.)
C
C A* REAL (LDA,N)
C real symmetric input matrix.
C Only the diagonal and upper triangle of A must be input,
C as SSIEV copies the upper triangle to the lower.
C That is, the user must define A(I,J), I=1,..N, and J=I,.
C ..,N.
C On return from SSIEV, if the user has set JOB
C = 0 the lower triangle of A has been altered.
C = nonzero the N eigenvectors of A are stored in its
C first N columns. See also INFO below.
C
C LDA INTEGER
C set by the user to
C the leading dimension of the array A.
C
C N INTEGER
C set by the user to
C the order of the matrix A and
C the number of elements in E.
C
C E* REAL (N)
C on return from SSIEV, E contains the N
C eigenvalues of A. See also INFO below.
C
C WORK* REAL (2*N)
C temporary storage vector. Contents changed by SSIEV.
C
C JOB INTEGER
C set by user on input
C = 0 only calculate eigenvalues of A.
C = nonzero calculate eigenvalues and eigenvectors of A.
C
C INFO* INTEGER
C on return from SSIEV, the value of INFO is
C = 0 for normal return.
C = K if the eigenvalue iteration fails to converge.
C eigenvalues and vectors 1 through K-1 are correct.
C
C
C Error Messages-
C No. 1 recoverable N is greater than LDA
C No. 2 recoverable N is less than one
C
C***REFERENCES (NONE)
C***ROUTINES CALLED IMTQL2, TQLRAT, TRED1, TRED2, XERMSG
C***REVISION HISTORY (YYMMDD)
C 800808 DATE WRITTEN
C 890831 Modified array declarations. (WRB)
C 890831 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
C 900326 Removed duplicate information from DESCRIPTION section.
C (WRB)
C***END PROLOGUE SSIEV