LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  ctgsja (JOBU, JOBV, JOBQ, M, P, N, K, L, A, LDA, B, LDB, TOLA, TOLB, ALPHA, BETA, U, LDU, V, LDV, Q, LDQ, WORK, NCYCLE, INFO) 
CTGSJA 
subroutine ctgsja  (  character  JOBU, 
character  JOBV,  
character  JOBQ,  
integer  M,  
integer  P,  
integer  N,  
integer  K,  
integer  L,  
complex, dimension( lda, * )  A,  
integer  LDA,  
complex, dimension( ldb, * )  B,  
integer  LDB,  
real  TOLA,  
real  TOLB,  
real, dimension( * )  ALPHA,  
real, dimension( * )  BETA,  
complex, dimension( ldu, * )  U,  
integer  LDU,  
complex, dimension( ldv, * )  V,  
integer  LDV,  
complex, dimension( ldq, * )  Q,  
integer  LDQ,  
complex, dimension( * )  WORK,  
integer  NCYCLE,  
integer  INFO  
) 
CTGSJA
Download CTGSJA + dependencies [TGZ] [ZIP] [TXT]CTGSJA computes the generalized singular value decomposition (GSVD) of two complex upper triangular (or trapezoidal) matrices A and B. On entry, it is assumed that matrices A and B have the following forms, which may be obtained by the preprocessing subroutine CGGSVP from a general MbyN matrix A and PbyN matrix B: NKL K L A = K ( 0 A12 A13 ) if MKL >= 0; L ( 0 0 A23 ) MKL ( 0 0 0 ) NKL K L A = K ( 0 A12 A13 ) if MKL < 0; MK ( 0 0 A23 ) NKL K L B = L ( 0 0 B13 ) PL ( 0 0 0 ) where the KbyK matrix A12 and LbyL matrix B13 are nonsingular upper triangular; A23 is LbyL upper triangular if MKL >= 0, otherwise A23 is (MK)byL upper trapezoidal. On exit, U**H *A*Q = D1*( 0 R ), V**H *B*Q = D2*( 0 R ), where U, V and Q are unitary matrices. R is a nonsingular upper triangular matrix, and D1 and D2 are ``diagonal'' matrices, which are of the following structures: If MKL >= 0, K L D1 = K ( I 0 ) L ( 0 C ) MKL ( 0 0 ) K L D2 = L ( 0 S ) PL ( 0 0 ) NKL K L ( 0 R ) = K ( 0 R11 R12 ) K L ( 0 0 R22 ) L where C = diag( ALPHA(K+1), ... , ALPHA(K+L) ), S = diag( BETA(K+1), ... , BETA(K+L) ), C**2 + S**2 = I. R is stored in A(1:K+L,NKL+1:N) on exit. If MKL < 0, K MK K+LM D1 = K ( I 0 0 ) MK ( 0 C 0 ) K MK K+LM D2 = MK ( 0 S 0 ) K+LM ( 0 0 I ) PL ( 0 0 0 ) NKL K MK K+LM ( 0 R ) = K ( 0 R11 R12 R13 ) MK ( 0 0 R22 R23 ) K+LM ( 0 0 0 R33 ) where C = diag( ALPHA(K+1), ... , ALPHA(M) ), S = diag( BETA(K+1), ... , BETA(M) ), C**2 + S**2 = I. R = ( R11 R12 R13 ) is stored in A(1:M, NKL+1:N) and R33 is stored ( 0 R22 R23 ) in B(MK+1:L,N+MKL+1:N) on exit. The computation of the unitary transformation matrices U, V or Q is optional. These matrices may either be formed explicitly, or they may be postmultiplied into input matrices U1, V1, or Q1.
[in]  JOBU  JOBU is CHARACTER*1 = 'U': U must contain a unitary matrix U1 on entry, and the product U1*U is returned; = 'I': U is initialized to the unit matrix, and the unitary matrix U is returned; = 'N': U is not computed. 
[in]  JOBV  JOBV is CHARACTER*1 = 'V': V must contain a unitary matrix V1 on entry, and the product V1*V is returned; = 'I': V is initialized to the unit matrix, and the unitary matrix V is returned; = 'N': V is not computed. 
[in]  JOBQ  JOBQ is CHARACTER*1 = 'Q': Q must contain a unitary matrix Q1 on entry, and the product Q1*Q is returned; = 'I': Q is initialized to the unit matrix, and the unitary matrix Q is returned; = 'N': Q is not computed. 
[in]  M  M is INTEGER The number of rows of the matrix A. M >= 0. 
[in]  P  P is INTEGER The number of rows of the matrix B. P >= 0. 
[in]  N  N is INTEGER The number of columns of the matrices A and B. N >= 0. 
[in]  K  K is INTEGER 
[in]  L  L is INTEGER K and L specify the subblocks in the input matrices A and B: A23 = A(K+1:MIN(K+L,M),NL+1:N) and B13 = B(1:L,,NL+1:N) of A and B, whose GSVD is going to be computed by CTGSJA. See Further Details. 
[in,out]  A  A is COMPLEX array, dimension (LDA,N) On entry, the MbyN matrix A. On exit, A(NK+1:N,1:MIN(K+L,M) ) contains the triangular matrix R or part of R. See Purpose for details. 
[in]  LDA  LDA is INTEGER The leading dimension of the array A. LDA >= max(1,M). 
[in,out]  B  B is COMPLEX array, dimension (LDB,N) On entry, the PbyN matrix B. On exit, if necessary, B(MK+1:L,N+MKL+1:N) contains a part of R. See Purpose for details. 
[in]  LDB  LDB is INTEGER The leading dimension of the array B. LDB >= max(1,P). 
[in]  TOLA  TOLA is REAL 
[in]  TOLB  TOLB is REAL TOLA and TOLB are the convergence criteria for the Jacobi Kogbetliantz iteration procedure. Generally, they are the same as used in the preprocessing step, say TOLA = MAX(M,N)*norm(A)*MACHEPS, TOLB = MAX(P,N)*norm(B)*MACHEPS. 
[out]  ALPHA  ALPHA is REAL array, dimension (N) 
[out]  BETA  BETA is REAL array, dimension (N) On exit, ALPHA and BETA contain the generalized singular value pairs of A and B; ALPHA(1:K) = 1, BETA(1:K) = 0, and if MKL >= 0, ALPHA(K+1:K+L) = diag(C), BETA(K+1:K+L) = diag(S), or if MKL < 0, ALPHA(K+1:M)= C, ALPHA(M+1:K+L)= 0 BETA(K+1:M) = S, BETA(M+1:K+L) = 1. Furthermore, if K+L < N, ALPHA(K+L+1:N) = 0 BETA(K+L+1:N) = 0. 
[in,out]  U  U is COMPLEX array, dimension (LDU,M) On entry, if JOBU = 'U', U must contain a matrix U1 (usually the unitary matrix returned by CGGSVP). On exit, if JOBU = 'I', U contains the unitary matrix U; if JOBU = 'U', U contains the product U1*U. If JOBU = 'N', U is not referenced. 
[in]  LDU  LDU is INTEGER The leading dimension of the array U. LDU >= max(1,M) if JOBU = 'U'; LDU >= 1 otherwise. 
[in,out]  V  V is COMPLEX array, dimension (LDV,P) On entry, if JOBV = 'V', V must contain a matrix V1 (usually the unitary matrix returned by CGGSVP). On exit, if JOBV = 'I', V contains the unitary matrix V; if JOBV = 'V', V contains the product V1*V. If JOBV = 'N', V is not referenced. 
[in]  LDV  LDV is INTEGER The leading dimension of the array V. LDV >= max(1,P) if JOBV = 'V'; LDV >= 1 otherwise. 
[in,out]  Q  Q is COMPLEX array, dimension (LDQ,N) On entry, if JOBQ = 'Q', Q must contain a matrix Q1 (usually the unitary matrix returned by CGGSVP). On exit, if JOBQ = 'I', Q contains the unitary matrix Q; if JOBQ = 'Q', Q contains the product Q1*Q. If JOBQ = 'N', Q is not referenced. 
[in]  LDQ  LDQ is INTEGER The leading dimension of the array Q. LDQ >= max(1,N) if JOBQ = 'Q'; LDQ >= 1 otherwise. 
[out]  WORK  WORK is COMPLEX array, dimension (2*N) 
[out]  NCYCLE  NCYCLE is INTEGER The number of cycles required for convergence. 
[out]  INFO  INFO is INTEGER = 0: successful exit < 0: if INFO = i, the ith argument had an illegal value. = 1: the procedure does not converge after MAXIT cycles. 
MAXIT INTEGER MAXIT specifies the total loops that the iterative procedure may take. If after MAXIT cycles, the routine fails to converge, we return INFO = 1.
CTGSJA essentially uses a variant of Kogbetliantz algorithm to reduce min(L,MK)byL triangular (or trapezoidal) matrix A23 and LbyL matrix B13 to the form: U1**H *A13*Q1 = C1*R1; V1**H *B13*Q1 = S1*R1, where U1, V1 and Q1 are unitary matrix. C1 and S1 are diagonal matrices satisfying C1**2 + S1**2 = I, and R1 is an LbyL nonsingular upper triangular matrix.
Definition at line 378 of file ctgsja.f.