SGEEV(3)

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

NAME
sgeev - Compute the eigenvalues and, optionally, the eigenvectors of a real general matrix.

LIBRARY
SLATEC

CATEGORY
D4A2

TYPE
SINGLE PRECISION (SGEEV-S, CGEEV-C)

KEYWORDS
EIGENVALUES, EIGENVECTORS, GENERAL MATRIX

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

DESCRIPTION
Abstract SGEEV computes the eigenvalues and, optionally, the eigenvectors of a general real matrix. Call Sequence Parameters- (The values of parameters marked with * (star) will be changed by SGEEV.) A* REAL(LDA,N) real nonsymmetric input matrix. LDA INTEGER set by the user to the leading dimension of the real array A. N INTEGER set by the user to the order of the matrices A and V, and the number of elements in E. E* COMPLEX(N) on return from SGEEV, E contains the eigenvalues of A. See also INFO below. V* COMPLEX(LDV,N) on return from SGEEV, 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. (Note that if the input matrix A is nearly degenerate, V may be badly conditioned, i.e., may have nearly dependent columns.) 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 SGEEV. JOB INTEGER set by the user to = 0 eigenvalues only to be calculated by SGEEV. Neither V nor LDV is referenced. = nonzero eigenvalues and vectors to be calculated. In this case, A & V must be distinct arrays. Also, if LDA .GT. LDV, SGEEV changes all the elements of A thru column N. If LDA < LDV, SGEEV 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 SGEEV. INFO* INTEGER on return from SGEEV the value of INFO is = 0 normal return, calculation successful. = K if the eigenvalue iteration fails to converge, eigenvalues K+1 through N are correct, but no eigenvectors were computed even if they were requested (JOB nonzero). Error Messages No. 1 recoverable N is greater than LDA No. 2 recoverable N is less than one. No. 3 recoverable JOB is nonzero and N is greater than LDV No. 4 warning LDA > LDV, elements of A other than the N by N input elements have been changed. No. 5 warning LDA < LDV, elements of V other than the N x N output elements have been changed.

REFERENCES
(NONE)

ROUTINES CALLED
BALANC, BALBAK, HQR, HQR2, ORTHES, ORTRAN, SCOPY, SCOPYM, XERMSG

REVISION HISTORY (YYMMDD)
800808 DATE WRITTEN
890531 Changed all specific intrinsics to generic. (WRB)
890531 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)