## table of contents

complex16SYauxiliary(3) | LAPACK | complex16SYauxiliary(3) |

# NAME¶

complex16SYauxiliary

# SYNOPSIS¶

## Functions¶

subroutine **zlaesy** (A, B, C, RT1, RT2, EVSCAL, CS1, SN1)

**ZLAESY** computes the eigenvalues and eigenvectors of a 2-by-2 complex
symmetric matrix. double precision function **zlansy** (NORM, UPLO, N, A,
LDA, WORK)

**ZLANSY** returns the value of the 1-norm, or the Frobenius norm, or the
infinity norm, or the element of largest absolute value of a complex
symmetric matrix. subroutine **zlaqsy** (UPLO, N, A, LDA, S, SCOND, AMAX,
EQUED)

**ZLAQSY** scales a symmetric/Hermitian matrix, using scaling factors
computed by spoequ. subroutine **zsymv** (UPLO, N, ALPHA, A, LDA, X,
INCX, BETA, Y, INCY)

**ZSYMV** computes a matrix-vector product for a complex symmetric matrix.
subroutine **zsyr** (UPLO, N, ALPHA, X, INCX, A, LDA)

**ZSYR** performs the symmetric rank-1 update of a complex symmetric
matrix. subroutine **zsyswapr** (UPLO, N, A, LDA, I1, I2)

**ZSYSWAPR** subroutine **ztgsy2** (TRANS, IJOB, M, N, A, LDA, B, LDB,
C, LDC, D, LDD, E, LDE, F, LDF, SCALE, RDSUM, RDSCAL, INFO)

**ZTGSY2** solves the generalized Sylvester equation (unblocked algorithm).

# Detailed Description¶

This is the group of complex16 auxiliary functions for SY matrices

# Function Documentation¶

## subroutine zlaesy (complex*16 A, complex*16 B, complex*16 C, complex*16 RT1, complex*16 RT2, complex*16 EVSCAL, complex*16 CS1, complex*16 SN1)¶

**ZLAESY** computes the eigenvalues and eigenvectors of a
2-by-2 complex symmetric matrix.

**Purpose:**

ZLAESY computes the eigendecomposition of a 2-by-2 symmetric matrix

( ( A, B );( B, C ) )

provided the norm of the matrix of eigenvectors is larger than

some threshold value.

RT1 is the eigenvalue of larger absolute value, and RT2 of

smaller absolute value. If the eigenvectors are computed, then

on return ( CS1, SN1 ) is the unit eigenvector for RT1, hence

[ CS1 SN1 ] . [ A B ] . [ CS1 -SN1 ] = [ RT1 0 ]

[ -SN1 CS1 ] [ B C ] [ SN1 CS1 ] [ 0 RT2 ]

**Parameters**

*A*

A is COMPLEX*16

The ( 1, 1 ) element of input matrix.

*B*

B is COMPLEX*16

The ( 1, 2 ) element of input matrix. The ( 2, 1 ) element

is also given by B, since the 2-by-2 matrix is symmetric.

*C*

C is COMPLEX*16

The ( 2, 2 ) element of input matrix.

*RT1*

RT1 is COMPLEX*16

The eigenvalue of larger modulus.

*RT2*

RT2 is COMPLEX*16

The eigenvalue of smaller modulus.

*EVSCAL*

EVSCAL is COMPLEX*16

The complex value by which the eigenvector matrix was scaled

to make it orthonormal. If EVSCAL is zero, the eigenvectors

were not computed. This means one of two things: the 2-by-2

matrix could not be diagonalized, or the norm of the matrix

of eigenvectors before scaling was larger than the threshold

value THRESH (set below).

*CS1*

CS1 is COMPLEX*16

*SN1*

SN1 is COMPLEX*16

If EVSCAL .NE. 0, ( CS1, SN1 ) is the unit right eigenvector

for RT1.

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

## double precision function zlansy (character NORM, character UPLO, integer N, complex*16, dimension( lda, * ) A, integer LDA, double precision, dimension( * ) WORK)¶

**ZLANSY** returns the value of the 1-norm, or the Frobenius
norm, or the infinity norm, or the element of largest absolute value of a
complex symmetric matrix.

**Purpose:**

ZLANSY returns the value of the one norm, or the Frobenius norm, or

the infinity norm, or the element of largest absolute value of a

complex symmetric matrix A.

**Returns**

ZLANSY = ( max(abs(A(i,j))), NORM = 'M' or 'm'

(

( norm1(A), NORM = '1', 'O' or 'o'

(

( normI(A), NORM = 'I' or 'i'

(

( normF(A), NORM = 'F', 'f', 'E' or 'e'

where norm1 denotes the one norm of a matrix (maximum column sum),

normI denotes the infinity norm of a matrix (maximum row sum) and

normF denotes the Frobenius norm of a matrix (square root of sum of

squares). Note that max(abs(A(i,j))) is not a consistent matrix norm.

**Parameters**

*NORM*

NORM is CHARACTER*1

Specifies the value to be returned in ZLANSY as described

above.

*UPLO*

UPLO is CHARACTER*1

Specifies whether the upper or lower triangular part of the

symmetric matrix A is to be referenced.

= 'U': Upper triangular part of A is referenced

= 'L': Lower triangular part of A is referenced

*N*

N is INTEGER

The order of the matrix A. N >= 0. When N = 0, ZLANSY is

set to zero.

*A*

A is COMPLEX*16 array, dimension (LDA,N)

The symmetric matrix A. If UPLO = 'U', the leading n by n

upper triangular part of A contains the upper triangular part

of the matrix A, and the strictly lower triangular part of A

is not referenced. If UPLO = 'L', the leading n by n lower

triangular part of A contains the lower triangular part of

the matrix A, and the strictly upper triangular part of A is

not referenced.

*LDA*

LDA is INTEGER

The leading dimension of the array A. LDA >= max(N,1).

*WORK*

WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK)),

where LWORK >= N when NORM = 'I' or '1' or 'O'; otherwise,

WORK is not referenced.

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

## subroutine zlaqsy (character UPLO, integer N, complex*16, dimension( lda, * ) A, integer LDA, double precision, dimension( * ) S, double precision SCOND, double precision AMAX, character EQUED)¶

**ZLAQSY** scales a symmetric/Hermitian matrix, using scaling
factors computed by spoequ.

**Purpose:**

ZLAQSY equilibrates a symmetric matrix A using the scaling factors

in the vector S.

**Parameters**

*UPLO*

UPLO is CHARACTER*1

Specifies whether the upper or lower triangular part of the

symmetric matrix A is stored.

= 'U': Upper triangular

= 'L': Lower triangular

*N*

N is INTEGER

The order of the matrix A. N >= 0.

*A*

A is COMPLEX*16 array, dimension (LDA,N)

On entry, the symmetric matrix A. If UPLO = 'U', the leading

n by n upper triangular part of A contains the upper

triangular part of the matrix A, and the strictly lower

triangular part of A is not referenced. If UPLO = 'L', the

leading n by n lower triangular part of A contains the lower

triangular part of the matrix A, and the strictly upper

triangular part of A is not referenced.

On exit, if EQUED = 'Y', the equilibrated matrix:

diag(S) * A * diag(S).

*LDA*

LDA is INTEGER

The leading dimension of the array A. LDA >= max(N,1).

*S*

S is DOUBLE PRECISION array, dimension (N)

The scale factors for A.

*SCOND*

SCOND is DOUBLE PRECISION

Ratio of the smallest S(i) to the largest S(i).

*AMAX*

AMAX is DOUBLE PRECISION

Absolute value of largest matrix entry.

*EQUED*

EQUED is CHARACTER*1

Specifies whether or not equilibration was done.

= 'N': No equilibration.

= 'Y': Equilibration was done, i.e., A has been replaced by

diag(S) * A * diag(S).

**Internal Parameters:**

THRESH is a threshold value used to decide if scaling should be done

based on the ratio of the scaling factors. If SCOND < THRESH,

scaling is done.

LARGE and SMALL are threshold values used to decide if scaling should

be done based on the absolute size of the largest matrix element.

If AMAX > LARGE or AMAX < SMALL, scaling is done.

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

## subroutine zsymv (character UPLO, integer N, complex*16 ALPHA, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( * ) X, integer INCX, complex*16 BETA, complex*16, dimension( * ) Y, integer INCY)¶

**ZSYMV** computes a matrix-vector product for a complex
symmetric matrix.

**Purpose:**

ZSYMV performs the matrix-vector operation

y := alpha*A*x + beta*y,

where alpha and beta are scalars, x and y are n element vectors and

A is an n by n symmetric matrix.

**Parameters**

*UPLO*

UPLO is CHARACTER*1

On entry, UPLO specifies whether the upper or lower

triangular part of the array A is to be referenced as

follows:

UPLO = 'U' or 'u' Only the upper triangular part of A

is to be referenced.

UPLO = 'L' or 'l' Only the lower triangular part of A

is to be referenced.

Unchanged on exit.

*N*

N is INTEGER

On entry, N specifies the order of the matrix A.

N must be at least zero.

Unchanged on exit.

*ALPHA*

ALPHA is COMPLEX*16

On entry, ALPHA specifies the scalar alpha.

Unchanged on exit.

*A*

A is COMPLEX*16 array, dimension ( LDA, N )

Before entry, with UPLO = 'U' or 'u', the leading n by n

upper triangular part of the array A must contain the upper

triangular part of the symmetric matrix and the strictly

lower triangular part of A is not referenced.

Before entry, with UPLO = 'L' or 'l', the leading n by n

lower triangular part of the array A must contain the lower

triangular part of the symmetric matrix and the strictly

upper triangular part of A is not referenced.

Unchanged on exit.

*LDA*

LDA is INTEGER

On entry, LDA specifies the first dimension of A as declared

in the calling (sub) program. LDA must be at least

max( 1, N ).

Unchanged on exit.

*X*

X is COMPLEX*16 array, dimension at least

( 1 + ( N - 1 )*abs( INCX ) ).

Before entry, the incremented array X must contain the N-

element vector x.

Unchanged on exit.

*INCX*

INCX is INTEGER

On entry, INCX specifies the increment for the elements of

X. INCX must not be zero.

Unchanged on exit.

*BETA*

BETA is COMPLEX*16

On entry, BETA specifies the scalar beta. When BETA is

supplied as zero then Y need not be set on input.

Unchanged on exit.

*Y*

Y is COMPLEX*16 array, dimension at least

( 1 + ( N - 1 )*abs( INCY ) ).

Before entry, the incremented array Y must contain the n

element vector y. On exit, Y is overwritten by the updated

vector y.

*INCY*

INCY is INTEGER

On entry, INCY specifies the increment for the elements of

Y. INCY must not be zero.

Unchanged on exit.

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

## subroutine zsyr (character UPLO, integer N, complex*16 ALPHA, complex*16, dimension( * ) X, integer INCX, complex*16, dimension( lda, * ) A, integer LDA)¶

**ZSYR** performs the symmetric rank-1 update of a complex
symmetric matrix.

**Purpose:**

ZSYR performs the symmetric rank 1 operation

A := alpha*x*x**H + A,

where alpha is a complex scalar, x is an n element vector and A is an

n by n symmetric matrix.

**Parameters**

*UPLO*

UPLO is CHARACTER*1

On entry, UPLO specifies whether the upper or lower

triangular part of the array A is to be referenced as

follows:

UPLO = 'U' or 'u' Only the upper triangular part of A

is to be referenced.

UPLO = 'L' or 'l' Only the lower triangular part of A

is to be referenced.

Unchanged on exit.

*N*

N is INTEGER

On entry, N specifies the order of the matrix A.

N must be at least zero.

Unchanged on exit.

*ALPHA*

ALPHA is COMPLEX*16

On entry, ALPHA specifies the scalar alpha.

Unchanged on exit.

*X*

X is COMPLEX*16 array, dimension at least

( 1 + ( N - 1 )*abs( INCX ) ).

Before entry, the incremented array X must contain the N-

element vector x.

Unchanged on exit.

*INCX*

INCX is INTEGER

On entry, INCX specifies the increment for the elements of

X. INCX must not be zero.

Unchanged on exit.

*A*

A is COMPLEX*16 array, dimension ( LDA, N )

Before entry, with UPLO = 'U' or 'u', the leading n by n

upper triangular part of the array A must contain the upper

triangular part of the symmetric matrix and the strictly

lower triangular part of A is not referenced. On exit, the

upper triangular part of the array A is overwritten by the

upper triangular part of the updated matrix.

Before entry, with UPLO = 'L' or 'l', the leading n by n

lower triangular part of the array A must contain the lower

triangular part of the symmetric matrix and the strictly

upper triangular part of A is not referenced. On exit, the

lower triangular part of the array A is overwritten by the

lower triangular part of the updated matrix.

*LDA*

LDA is INTEGER

On entry, LDA specifies the first dimension of A as declared

in the calling (sub) program. LDA must be at least

max( 1, N ).

Unchanged on exit.

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

## subroutine zsyswapr (character UPLO, integer N, complex*16, dimension( lda, n ) A, integer LDA, integer I1, integer I2)¶

**ZSYSWAPR**

**Purpose:**

ZSYSWAPR applies an elementary permutation on the rows and the columns of

a symmetric matrix.

**Parameters**

*UPLO*

UPLO is CHARACTER*1

Specifies whether the details of the factorization are stored

as an upper or lower triangular matrix.

= 'U': Upper triangular, form is A = U*D*U**T;

= 'L': Lower triangular, form is A = L*D*L**T.

*N*

N is INTEGER

The order of the matrix A. N >= 0.

*A*

A is COMPLEX*16 array, dimension (LDA,N)

On entry, the NB diagonal matrix D and the multipliers

used to obtain the factor U or L as computed by ZSYTRF.

On exit, if INFO = 0, the (symmetric) inverse of the original

matrix. If UPLO = 'U', the upper triangular part of the

inverse is formed and the part of A below the diagonal is not

referenced; if UPLO = 'L' the lower triangular part of the

inverse is formed and the part of A above the diagonal is

not referenced.

*LDA*

LDA is INTEGER

The leading dimension of the array A. LDA >= max(1,N).

*I1*

I1 is INTEGER

Index of the first row to swap

*I2*

I2 is INTEGER

Index of the second row to swap

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

## subroutine ztgsy2 (character TRANS, integer IJOB, integer M, integer N, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( ldb, * ) B, integer LDB, complex*16, dimension( ldc, * ) C, integer LDC, complex*16, dimension( ldd, * ) D, integer LDD, complex*16, dimension( lde, * ) E, integer LDE, complex*16, dimension( ldf, * ) F, integer LDF, double precision SCALE, double precision RDSUM, double precision RDSCAL, integer INFO)¶

**ZTGSY2** solves the generalized Sylvester equation (unblocked
algorithm).

**Purpose:**

ZTGSY2 solves the generalized Sylvester equation

A * R - L * B = scale * C (1)

D * R - L * E = scale * F

using Level 1 and 2 BLAS, where R and L are unknown M-by-N matrices,

(A, D), (B, E) and (C, F) are given matrix pairs of size M-by-M,

N-by-N and M-by-N, respectively. A, B, D and E are upper triangular

(i.e., (A,D) and (B,E) in generalized Schur form).

The solution (R, L) overwrites (C, F). 0 <= SCALE <= 1 is an output

scaling factor chosen to avoid overflow.

In matrix notation solving equation (1) corresponds to solve

Zx = scale * b, where Z is defined as

Z = [ kron(In, A) -kron(B**H, Im) ] (2)

[ kron(In, D) -kron(E**H, Im) ],

Ik is the identity matrix of size k and X**H is the conjuguate transpose of X.

kron(X, Y) is the Kronecker product between the matrices X and Y.

If TRANS = 'C', y in the conjugate transposed system Z**H*y = scale*b

is solved for, which is equivalent to solve for R and L in

A**H * R + D**H * L = scale * C (3)

R * B**H + L * E**H = scale * -F

This case is used to compute an estimate of Dif[(A, D), (B, E)] =

= sigma_min(Z) using reverse communication with ZLACON.

ZTGSY2 also (IJOB >= 1) contributes to the computation in ZTGSYL

of an upper bound on the separation between to matrix pairs. Then

the input (A, D), (B, E) are sub-pencils of two matrix pairs in

ZTGSYL.

**Parameters**

*TRANS*

TRANS is CHARACTER*1

= 'N': solve the generalized Sylvester equation (1).

= 'T': solve the 'transposed' system (3).

*IJOB*

IJOB is INTEGER

Specifies what kind of functionality to be performed.

=0: solve (1) only.

=1: A contribution from this subsystem to a Frobenius

norm-based estimate of the separation between two matrix

pairs is computed. (look ahead strategy is used).

=2: A contribution from this subsystem to a Frobenius

norm-based estimate of the separation between two matrix

pairs is computed. (DGECON on sub-systems is used.)

Not referenced if TRANS = 'T'.

*M*

M is INTEGER

On entry, M specifies the order of A and D, and the row

dimension of C, F, R and L.

*N*

N is INTEGER

On entry, N specifies the order of B and E, and the column

dimension of C, F, R and L.

*A*

A is COMPLEX*16 array, dimension (LDA, M)

On entry, A contains an upper triangular matrix.

*LDA*

LDA is INTEGER

The leading dimension of the matrix A. LDA >= max(1, M).

*B*

B is COMPLEX*16 array, dimension (LDB, N)

On entry, B contains an upper triangular matrix.

*LDB*

LDB is INTEGER

The leading dimension of the matrix B. LDB >= max(1, N).

*C*

C is COMPLEX*16 array, dimension (LDC, N)

On entry, C contains the right-hand-side of the first matrix

equation in (1).

On exit, if IJOB = 0, C has been overwritten by the solution

R.

*LDC*

LDC is INTEGER

The leading dimension of the matrix C. LDC >= max(1, M).

*D*

D is COMPLEX*16 array, dimension (LDD, M)

On entry, D contains an upper triangular matrix.

*LDD*

LDD is INTEGER

The leading dimension of the matrix D. LDD >= max(1, M).

*E*

E is COMPLEX*16 array, dimension (LDE, N)

On entry, E contains an upper triangular matrix.

*LDE*

LDE is INTEGER

The leading dimension of the matrix E. LDE >= max(1, N).

*F*

F is COMPLEX*16 array, dimension (LDF, N)

On entry, F contains the right-hand-side of the second matrix

equation in (1).

On exit, if IJOB = 0, F has been overwritten by the solution

L.

*LDF*

LDF is INTEGER

The leading dimension of the matrix F. LDF >= max(1, M).

*SCALE*

SCALE is DOUBLE PRECISION

On exit, 0 <= SCALE <= 1. If 0 < SCALE < 1, the solutions

R and L (C and F on entry) will hold the solutions to a

slightly perturbed system but the input matrices A, B, D and

E have not been changed. If SCALE = 0, R and L will hold the

solutions to the homogeneous system with C = F = 0.

Normally, SCALE = 1.

*RDSUM*

RDSUM is DOUBLE PRECISION

On entry, the sum of squares of computed contributions to

the Dif-estimate under computation by ZTGSYL, where the

scaling factor RDSCAL (see below) has been factored out.

On exit, the corresponding sum of squares updated with the

contributions from the current sub-system.

If TRANS = 'T' RDSUM is not touched.

NOTE: RDSUM only makes sense when ZTGSY2 is called by

ZTGSYL.

*RDSCAL*

RDSCAL is DOUBLE PRECISION

On entry, scaling factor used to prevent overflow in RDSUM.

On exit, RDSCAL is updated w.r.t. the current contributions

in RDSUM.

If TRANS = 'T', RDSCAL is not touched.

NOTE: RDSCAL only makes sense when ZTGSY2 is called by

ZTGSYL.

*INFO*

INFO is INTEGER

On exit, if INFO is set to

=0: Successful exit

<0: If INFO = -i, input argument number i is illegal.

>0: The matrix pairs (A, D) and (B, E) have common or very

close eigenvalues.

**Author**

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date**

**Contributors:**

# Author¶

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