*DECK TRISP SUBROUTINE TRISP (N, A, B, C, D, U, Z) C***BEGIN PROLOGUE TRISP C***SUBSIDIARY C***PURPOSE Subsidiary to SEPELI C***LIBRARY SLATEC C***TYPE SINGLE PRECISION (TRISP-S) C***AUTHOR (UNKNOWN) C***DESCRIPTION C C This subroutine solves for a non-zero eigenvector corresponding C to the zero eigenvalue of the transpose of the rank C deficient ONE matrix with subdiagonal A, diagonal B, and C superdiagonal C , with A(1) in the (1,N) position, with C C(N) in the (N,1) position, and all other elements zero. C C***SEE ALSO SEPELI C***ROUTINES CALLED (NONE) C***REVISION HISTORY (YYMMDD) C 801001 DATE WRITTEN C 890831 Modified array declarations. (WRB) C 891214 Prologue converted to Version 4.0 format. (BAB) C 900402 Added TYPE section. (WRB) C***END PROLOGUE TRISP C DIMENSION A(*) ,B(*) ,C(*) ,D(*) , 1 U(*) ,Z(*) C***FIRST EXECUTABLE STATEMENT TRISP BN = B(N) D(1) = A(2)/B(1) V = A(1) U(1) = C(N)/B(1) NM2 = N-2 DO 10 J=2,NM2 DEN = B(J)-C(J-1)*D(J-1) D(J) = A(J+1)/DEN U(J) = -C(J-1)*U(J-1)/DEN BN = BN-V*U(J-1) V = -V*D(J-1) 10 CONTINUE DEN = B(N-1)-C(N-2)*D(N-2) D(N-1) = (A(N)-C(N-2)*U(N-2))/DEN AN = C(N-1)-V*D(N-2) BN = BN-V*U(N-2) DEN = BN-AN*D(N-1) C C SET LAST COMPONENT EQUAL TO ONE C Z(N) = 1.0 Z(N-1) = -D(N-1) NM1 = N-1 DO 20 J=2,NM1 K = N-J Z(K) = -D(K)*Z(K+1)-U(K)*Z(N) 20 CONTINUE RETURN END