SUBROUTINE ZTRSYL( TRANA, TRANB, ISGN, M, N, A, LDA, B, LDB, C, \$ LDC, SCALE, INFO ) * * -- LAPACK routine (version 3.0) -- * Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., * Courant Institute, Argonne National Lab, and Rice University * January 9, 2001 * * .. Scalar Arguments .. CHARACTER TRANA, TRANB INTEGER INFO, ISGN, LDA, LDB, LDC, M, N DOUBLE PRECISION SCALE * .. * .. Array Arguments .. COMPLEX*16 A( LDA, * ), B( LDB, * ), C( LDC, * ) * .. * * Purpose * ======= * * ZTRSYL solves the complex Sylvester matrix equation: * * op(A)*X + X*op(B) = scale*C or * op(A)*X - X*op(B) = scale*C, * * where op(A) = A or A**H, and A and B are both upper triangular. A is * M-by-M and B is N-by-N; the right hand side C and the solution X are * M-by-N; and scale is an output scale factor, set <= 1 to avoid * overflow in X. * * Arguments * ========= * * TRANA (input) CHARACTER*1 * Specifies the option op(A): * = 'N': op(A) = A (No transpose) * = 'C': op(A) = A**H (Conjugate transpose) * * TRANB (input) CHARACTER*1 * Specifies the option op(B): * = 'N': op(B) = B (No transpose) * = 'C': op(B) = B**H (Conjugate transpose) * * ISGN (input) INTEGER * Specifies the sign in the equation: * = +1: solve op(A)*X + X*op(B) = scale*C * = -1: solve op(A)*X - X*op(B) = scale*C * * M (input) INTEGER * The order of the matrix A, and the number of rows in the * matrices X and C. M >= 0. * * N (input) INTEGER * The order of the matrix B, and the number of columns in the * matrices X and C. N >= 0. * * A (input) COMPLEX*16 array, dimension (LDA,M) * The upper triangular matrix A. * * LDA (input) INTEGER * The leading dimension of the array A. LDA >= max(1,M). * * B (input) COMPLEX*16 array, dimension (LDB,N) * The upper triangular matrix B. * * LDB (input) INTEGER * The leading dimension of the array B. LDB >= max(1,N). * * C (input/output) COMPLEX*16 array, dimension (LDC,N) * On entry, the M-by-N right hand side matrix C. * On exit, C is overwritten by the solution matrix X. * * LDC (input) INTEGER * The leading dimension of the array C. LDC >= max(1,M) * * SCALE (output) DOUBLE PRECISION * The scale factor, scale, set <= 1 to avoid overflow in X. * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -i, the i-th argument had an illegal value * = 1: A and B have common or very close eigenvalues; perturbed * values were used to solve the equation (but the matrices * A and B are unchanged). * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ONE PARAMETER ( ONE = 1.0D+0 ) * .. * .. Local Scalars .. LOGICAL NOTRNA, NOTRNB INTEGER J, K, L DOUBLE PRECISION BIGNUM, DA11, DB, EPS, SCALOC, SGN, SMIN, \$ SMLNUM COMPLEX*16 A11, SUML, SUMR, VEC, X11 * .. * .. Local Arrays .. DOUBLE PRECISION DUM( 1 ) * .. * .. External Functions .. LOGICAL LSAME DOUBLE PRECISION DLAMCH, ZLANGE COMPLEX*16 ZDOTC, ZDOTU, ZLADIV EXTERNAL LSAME, DLAMCH, ZLANGE, ZDOTC, ZDOTU, ZLADIV * .. * .. External Subroutines .. EXTERNAL XERBLA, ZDSCAL * .. * .. Intrinsic Functions .. INTRINSIC ABS, DBLE, DCMPLX, DCONJG, DIMAG, MAX, MIN * .. * .. Executable Statements .. * * Decode and Test input parameters * NOTRNA = LSAME( TRANA, 'N' ) NOTRNB = LSAME( TRANB, 'N' ) * INFO = 0 IF( .NOT.NOTRNA .AND. .NOT.LSAME( TRANA, 'C' ) ) THEN INFO = -1 ELSE IF( .NOT.NOTRNB .AND. .NOT.LSAME( TRANB, 'C' ) ) THEN INFO = -2 ELSE IF( ISGN.NE.1 .AND. ISGN.NE.-1 ) THEN INFO = -3 ELSE IF( M.LT.0 ) THEN INFO = -4 ELSE IF( N.LT.0 ) THEN INFO = -5 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN INFO = -7 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN INFO = -9 ELSE IF( LDC.LT.MAX( 1, M ) ) THEN INFO = -11 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'ZTRSYL', -INFO ) RETURN END IF * * Quick return if possible * IF( M.EQ.0 .OR. N.EQ.0 ) \$ RETURN * * Set constants to control overflow * EPS = DLAMCH( 'P' ) SMLNUM = DLAMCH( 'S' ) BIGNUM = ONE / SMLNUM CALL DLABAD( SMLNUM, BIGNUM ) SMLNUM = SMLNUM*DBLE( M*N ) / EPS BIGNUM = ONE / SMLNUM SMIN = MAX( SMLNUM, EPS*ZLANGE( 'M', M, M, A, LDA, DUM ), \$ EPS*ZLANGE( 'M', N, N, B, LDB, DUM ) ) SCALE = ONE SGN = ISGN * IF( NOTRNA .AND. NOTRNB ) THEN * * Solve A*X + ISGN*X*B = scale*C. * * The (K,L)th block of X is determined starting from * bottom-left corner column by column by * * A(K,K)*X(K,L) + ISGN*X(K,L)*B(L,L) = C(K,L) - R(K,L) * * Where * M L-1 * R(K,L) = SUM [A(K,I)*X(I,L)] +ISGN*SUM [X(K,J)*B(J,L)]. * I=K+1 J=1 * DO 30 L = 1, N DO 20 K = M, 1, -1 * SUML = ZDOTU( M-K, A( K, MIN( K+1, M ) ), LDA, \$ C( MIN( K+1, M ), L ), 1 ) SUMR = ZDOTU( L-1, C( K, 1 ), LDC, B( 1, L ), 1 ) VEC = C( K, L ) - ( SUML+SGN*SUMR ) * SCALOC = ONE A11 = A( K, K ) + SGN*B( L, L ) DA11 = ABS( DBLE( A11 ) ) + ABS( DIMAG( A11 ) ) IF( DA11.LE.SMIN ) THEN A11 = SMIN DA11 = SMIN INFO = 1 END IF DB = ABS( DBLE( VEC ) ) + ABS( DIMAG( VEC ) ) IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN IF( DB.GT.BIGNUM*DA11 ) \$ SCALOC = ONE / DB END IF X11 = ZLADIV( VEC*DCMPLX( SCALOC ), A11 ) * IF( SCALOC.NE.ONE ) THEN DO 10 J = 1, N CALL ZDSCAL( M, SCALOC, C( 1, J ), 1 ) 10 CONTINUE SCALE = SCALE*SCALOC END IF C( K, L ) = X11 * 20 CONTINUE 30 CONTINUE * ELSE IF( .NOT.NOTRNA .AND. NOTRNB ) THEN * * Solve A' *X + ISGN*X*B = scale*C. * * The (K,L)th block of X is determined starting from * upper-left corner column by column by * * A'(K,K)*X(K,L) + ISGN*X(K,L)*B(L,L) = C(K,L) - R(K,L) * * Where * K-1 L-1 * R(K,L) = SUM [A'(I,K)*X(I,L)] + ISGN*SUM [X(K,J)*B(J,L)] * I=1 J=1 * DO 60 L = 1, N DO 50 K = 1, M * SUML = ZDOTC( K-1, A( 1, K ), 1, C( 1, L ), 1 ) SUMR = ZDOTU( L-1, C( K, 1 ), LDC, B( 1, L ), 1 ) VEC = C( K, L ) - ( SUML+SGN*SUMR ) * SCALOC = ONE A11 = DCONJG( A( K, K ) ) + SGN*B( L, L ) DA11 = ABS( DBLE( A11 ) ) + ABS( DIMAG( A11 ) ) IF( DA11.LE.SMIN ) THEN A11 = SMIN DA11 = SMIN INFO = 1 END IF DB = ABS( DBLE( VEC ) ) + ABS( DIMAG( VEC ) ) IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN IF( DB.GT.BIGNUM*DA11 ) \$ SCALOC = ONE / DB END IF * X11 = ZLADIV( VEC*DCMPLX( SCALOC ), A11 ) * IF( SCALOC.NE.ONE ) THEN DO 40 J = 1, N CALL ZDSCAL( M, SCALOC, C( 1, J ), 1 ) 40 CONTINUE SCALE = SCALE*SCALOC END IF C( K, L ) = X11 * 50 CONTINUE 60 CONTINUE * ELSE IF( .NOT.NOTRNA .AND. .NOT.NOTRNB ) THEN * * Solve A'*X + ISGN*X*B' = C. * * The (K,L)th block of X is determined starting from * upper-right corner column by column by * * A'(K,K)*X(K,L) + ISGN*X(K,L)*B'(L,L) = C(K,L) - R(K,L) * * Where * K-1 * R(K,L) = SUM [A'(I,K)*X(I,L)] + * I=1 * N * ISGN*SUM [X(K,J)*B'(L,J)]. * J=L+1 * DO 90 L = N, 1, -1 DO 80 K = 1, M * SUML = ZDOTC( K-1, A( 1, K ), 1, C( 1, L ), 1 ) SUMR = ZDOTC( N-L, C( K, MIN( L+1, N ) ), LDC, \$ B( L, MIN( L+1, N ) ), LDB ) VEC = C( K, L ) - ( SUML+SGN*DCONJG( SUMR ) ) * SCALOC = ONE A11 = DCONJG( A( K, K )+SGN*B( L, L ) ) DA11 = ABS( DBLE( A11 ) ) + ABS( DIMAG( A11 ) ) IF( DA11.LE.SMIN ) THEN A11 = SMIN DA11 = SMIN INFO = 1 END IF DB = ABS( DBLE( VEC ) ) + ABS( DIMAG( VEC ) ) IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN IF( DB.GT.BIGNUM*DA11 ) \$ SCALOC = ONE / DB END IF * X11 = ZLADIV( VEC*DCMPLX( SCALOC ), A11 ) * IF( SCALOC.NE.ONE ) THEN DO 70 J = 1, N CALL ZDSCAL( M, SCALOC, C( 1, J ), 1 ) 70 CONTINUE SCALE = SCALE*SCALOC END IF C( K, L ) = X11 * 80 CONTINUE 90 CONTINUE * ELSE IF( NOTRNA .AND. .NOT.NOTRNB ) THEN * * Solve A*X + ISGN*X*B' = C. * * The (K,L)th block of X is determined starting from * bottom-left corner column by column by * * A(K,K)*X(K,L) + ISGN*X(K,L)*B'(L,L) = C(K,L) - R(K,L) * * Where * M N * R(K,L) = SUM [A(K,I)*X(I,L)] + ISGN*SUM [X(K,J)*B'(L,J)] * I=K+1 J=L+1 * DO 120 L = N, 1, -1 DO 110 K = M, 1, -1 * SUML = ZDOTU( M-K, A( K, MIN( K+1, M ) ), LDA, \$ C( MIN( K+1, M ), L ), 1 ) SUMR = ZDOTC( N-L, C( K, MIN( L+1, N ) ), LDC, \$ B( L, MIN( L+1, N ) ), LDB ) VEC = C( K, L ) - ( SUML+SGN*DCONJG( SUMR ) ) * SCALOC = ONE A11 = A( K, K ) + SGN*DCONJG( B( L, L ) ) DA11 = ABS( DBLE( A11 ) ) + ABS( DIMAG( A11 ) ) IF( DA11.LE.SMIN ) THEN A11 = SMIN DA11 = SMIN INFO = 1 END IF DB = ABS( DBLE( VEC ) ) + ABS( DIMAG( VEC ) ) IF( DA11.LT.ONE .AND. DB.GT.ONE ) THEN IF( DB.GT.BIGNUM*DA11 ) \$ SCALOC = ONE / DB END IF * X11 = ZLADIV( VEC*DCMPLX( SCALOC ), A11 ) * IF( SCALOC.NE.ONE ) THEN DO 100 J = 1, N CALL ZDSCAL( M, SCALOC, C( 1, J ), 1 ) 100 CONTINUE SCALE = SCALE*SCALOC END IF C( K, L ) = X11 * 110 CONTINUE 120 CONTINUE * END IF * RETURN * * End of ZTRSYL * END