SSPEV(3)

SYNOPSIS
SUBROUTINE SSPEV (A, N, E, V, LDV, WORK, JOB, INFO)

NAME
sspev - Compute the eigenvalues and, optionally, the eigenvectors of a real symmetric matrix stored in packed form.

LIBRARY
SLATEC (EISPACK)

CATEGORY
D4A1

TYPE
SINGLE PRECISION (SSPEV-S)

KEYWORDS
EIGENVALUES, EIGENVECTORS, EISPACK, PACKED, SYMMETRIC

AUTHOR
Kahaner, D. K., (NBS) Moler, C. B., (U. of New Mexico) Stewart, G. W., (U. of Maryland)

DESCRIPTION
Abstract SSPEV computes the eigenvalues and, optionally, the eigenvectors of a real symmetric matrix stored in packed form. Call Sequence Parameters- (The values of parameters marked with * (star) will be changed by SSPEV.) A* REAL(N*(N+1)/2) real symmetric packed input matrix. Contains upper triangle and diagonal of A, by column (elements 11, 12, 22, 13, 23, 33, ...). N INTEGER set by the user to the order of the matrix A. E* REAL(N) on return from SSPEV, E contains the eigenvalues of A. See also INFO below. V* REAL(LDV,N) on return from SSPEV, if the user has set JOB = 0 V is not referenced. = nonzero the N eigenvectors of A are stored in the first N columns of V. See also INFO below. LDV INTEGER set by the user to the leading dimension of the array V if JOB is also set nonzero. In that case, N must be .LE. LDV. If JOB is set to zero, LDV is not referenced. WORK* REAL(2N) temporary storage vector. Contents changed by SSPEV. JOB INTEGER set by the user to = 0 eigenvalues only to be calculated by SSPEV. Neither V nor LDV are referenced. = nonzero eigenvalues and vectors to be calculated. In this case, A & V must be distinct arrays. Also, if LDA .GT. LDV, SSPEV changes all the elements of A thru column N. If LDA < LDV, SSPEV changes all the elements of V through column N. If LDA=LDV, only A(I,J) and V(I, J) for I,J = 1,...,N are changed by SSPEV. INFO* INTEGER on return from SSPEV, the value of INFO is = 0 for normal return. = K if the eigenvalue iteration fails to converge. Eigenvalues and vectors 1 through K-1 are correct. Error Messages- No. 1 recoverable N is greater than LDV and JOB is nonzero No. 2 recoverable N is less than one

REFERENCES
(NONE)

ROUTINES CALLED
IMTQL2, TQLRAT, TRBAK3, TRED3, XERMSG

REVISION HISTORY (YYMMDD)
800808 DATE WRITTEN
890831 Modified array declarations. (WRB)
890831 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
900326 Removed duplicate information from DESCRIPTION section. (WRB)