# zchkst2stg.f - Man Page

TESTING/EIG/zchkst2stg.f

## Synopsis

### Functions/Subroutines

subroutine **zchkst2stg** (nsizes, nn, ntypes, dotype, iseed, thresh, nounit, a, lda, ap, sd, se, d1, d2, d3, d4, d5, wa1, wa2, wa3, wr, u, ldu, v, vp, tau, z, work, lwork, rwork, lrwork, iwork, liwork, result, info)**ZCHKST2STG**

## Function/Subroutine Documentation

### subroutine zchkst2stg (integer nsizes, integer, dimension( * ) nn, integer ntypes, logical, dimension( * ) dotype, integer, dimension( 4 ) iseed, double precision thresh, integer nounit, complex*16, dimension( lda, * ) a, integer lda, complex*16, dimension( * ) ap, double precision, dimension( * ) sd, double precision, dimension( * ) se, double precision, dimension( * ) d1, double precision, dimension( * ) d2, double precision, dimension( * ) d3, double precision, dimension( * ) d4, double precision, dimension( * ) d5, double precision, dimension( * ) wa1, double precision, dimension( * ) wa2, double precision, dimension( * ) wa3, double precision, dimension( * ) wr, complex*16, dimension( ldu, * ) u, integer ldu, complex*16, dimension( ldu, * ) v, complex*16, dimension( * ) vp, complex*16, dimension( * ) tau, complex*16, dimension( ldu, * ) z, complex*16, dimension( * ) work, integer lwork, double precision, dimension( * ) rwork, integer lrwork, integer, dimension( * ) iwork, integer liwork, double precision, dimension( * ) result, integer info)

**ZCHKST2STG**

**Purpose:**

ZCHKST2STG checks the Hermitian eigenvalue problem routines using the 2-stage reduction techniques. Since the generation of Q or the vectors is not available in this release, we only compare the eigenvalue resulting when using the 2-stage to the one considered as reference using the standard 1-stage reduction ZHETRD. For that, we call the standard ZHETRD and compute D1 using DSTEQR, then we call the 2-stage ZHETRD_2STAGE with Upper and Lower and we compute D2 and D3 using DSTEQR and then we replaced tests 3 and 4 by tests 11 and 12. test 1 and 2 remain to verify that the 1-stage results are OK and can be trusted. This testing routine will converge to the ZCHKST in the next release when vectors and generation of Q will be implemented. ZHETRD factors A as U S U* , where * means conjugate transpose, S is real symmetric tridiagonal, and U is unitary. ZHETRD can use either just the lower or just the upper triangle of A; ZCHKST2STG checks both cases. U is represented as a product of Householder transformations, whose vectors are stored in the first n-1 columns of V, and whose scale factors are in TAU. ZHPTRD does the same as ZHETRD, except that A and V are stored in 'packed' format. ZUNGTR constructs the matrix U from the contents of V and TAU. ZUPGTR constructs the matrix U from the contents of VP and TAU. ZSTEQR factors S as Z D1 Z* , where Z is the unitary matrix of eigenvectors and D1 is a diagonal matrix with the eigenvalues on the diagonal. D2 is the matrix of eigenvalues computed when Z is not computed. DSTERF computes D3, the matrix of eigenvalues, by the PWK method, which does not yield eigenvectors. ZPTEQR factors S as Z4 D4 Z4* , for a Hermitian positive definite tridiagonal matrix. D5 is the matrix of eigenvalues computed when Z is not computed. DSTEBZ computes selected eigenvalues. WA1, WA2, and WA3 will denote eigenvalues computed to high absolute accuracy, with different range options. WR will denote eigenvalues computed to high relative accuracy. ZSTEIN computes Y, the eigenvectors of S, given the eigenvalues. ZSTEDC factors S as Z D1 Z* , where Z is the unitary matrix of eigenvectors and D1 is a diagonal matrix with the eigenvalues on the diagonal ('I' option). It may also update an input unitary matrix, usually the output from ZHETRD/ZUNGTR or ZHPTRD/ZUPGTR ('V' option). It may also just compute eigenvalues ('N' option). ZSTEMR factors S as Z D1 Z* , where Z is the unitary matrix of eigenvectors and D1 is a diagonal matrix with the eigenvalues on the diagonal ('I' option). ZSTEMR uses the Relatively Robust Representation whenever possible. When ZCHKST2STG is called, a number of matrix 'sizes' ('n's') and a number of matrix 'types' are specified. For each size ('n') and each type of matrix, one matrix will be generated and used to test the Hermitian eigenroutines. For each matrix, a number of tests will be performed: (1) | A - V S V* | / ( |A| n ulp ) ZHETRD( UPLO='U', ... ) (2) | I - UV* | / ( n ulp ) ZUNGTR( UPLO='U', ... ) (3) | A - V S V* | / ( |A| n ulp ) ZHETRD( UPLO='L', ... ) replaced by | D1 - D2 | / ( |D1| ulp ) where D1 is the eigenvalue matrix computed using S and D2 is the eigenvalue matrix computed using S_2stage the output of ZHETRD_2STAGE('N', 'U',....). D1 and D2 are computed via DSTEQR('N',...) (4) | I - UV* | / ( n ulp ) ZUNGTR( UPLO='L', ... ) replaced by | D1 - D3 | / ( |D1| ulp ) where D1 is the eigenvalue matrix computed using S and D3 is the eigenvalue matrix computed using S_2stage the output of ZHETRD_2STAGE('N', 'L',....). D1 and D3 are computed via DSTEQR('N',...) (5-8) Same as 1-4, but for ZHPTRD and ZUPGTR. (9) | S - Z D Z* | / ( |S| n ulp ) ZSTEQR('V',...) (10) | I - ZZ* | / ( n ulp ) ZSTEQR('V',...) (11) | D1 - D2 | / ( |D1| ulp ) ZSTEQR('N',...) (12) | D1 - D3 | / ( |D1| ulp ) DSTERF (13) 0 if the true eigenvalues (computed by sturm count) of S are within THRESH of those in D1. 2*THRESH if they are not. (Tested using DSTECH) For S positive definite, (14) | S - Z4 D4 Z4* | / ( |S| n ulp ) ZPTEQR('V',...) (15) | I - Z4 Z4* | / ( n ulp ) ZPTEQR('V',...) (16) | D4 - D5 | / ( 100 |D4| ulp ) ZPTEQR('N',...) When S is also diagonally dominant by the factor gamma < 1, (17) max | D4(i) - WR(i) | / ( |D4(i)| omega ) , i omega = 2 (2n-1) ULP (1 + 8 gamma**2) / (1 - gamma)**4 DSTEBZ( 'A', 'E', ...) (18) | WA1 - D3 | / ( |D3| ulp ) DSTEBZ( 'A', 'E', ...) (19) ( max { min | WA2(i)-WA3(j) | } + i j max { min | WA3(i)-WA2(j) | } ) / ( |D3| ulp ) i j DSTEBZ( 'I', 'E', ...) (20) | S - Y WA1 Y* | / ( |S| n ulp ) DSTEBZ, ZSTEIN (21) | I - Y Y* | / ( n ulp ) DSTEBZ, ZSTEIN (22) | S - Z D Z* | / ( |S| n ulp ) ZSTEDC('I') (23) | I - ZZ* | / ( n ulp ) ZSTEDC('I') (24) | S - Z D Z* | / ( |S| n ulp ) ZSTEDC('V') (25) | I - ZZ* | / ( n ulp ) ZSTEDC('V') (26) | D1 - D2 | / ( |D1| ulp ) ZSTEDC('V') and ZSTEDC('N') Test 27 is disabled at the moment because ZSTEMR does not guarantee high relatvie accuracy. (27) max | D6(i) - WR(i) | / ( |D6(i)| omega ) , i omega = 2 (2n-1) ULP (1 + 8 gamma**2) / (1 - gamma)**4 ZSTEMR('V', 'A') (28) max | D6(i) - WR(i) | / ( |D6(i)| omega ) , i omega = 2 (2n-1) ULP (1 + 8 gamma**2) / (1 - gamma)**4 ZSTEMR('V', 'I') Tests 29 through 34 are disable at present because ZSTEMR does not handle partial spectrum requests. (29) | S - Z D Z* | / ( |S| n ulp ) ZSTEMR('V', 'I') (30) | I - ZZ* | / ( n ulp ) ZSTEMR('V', 'I') (31) ( max { min | WA2(i)-WA3(j) | } + i j max { min | WA3(i)-WA2(j) | } ) / ( |D3| ulp ) i j ZSTEMR('N', 'I') vs. CSTEMR('V', 'I') (32) | S - Z D Z* | / ( |S| n ulp ) ZSTEMR('V', 'V') (33) | I - ZZ* | / ( n ulp ) ZSTEMR('V', 'V') (34) ( max { min | WA2(i)-WA3(j) | } + i j max { min | WA3(i)-WA2(j) | } ) / ( |D3| ulp ) i j ZSTEMR('N', 'V') vs. CSTEMR('V', 'V') (35) | S - Z D Z* | / ( |S| n ulp ) ZSTEMR('V', 'A') (36) | I - ZZ* | / ( n ulp ) ZSTEMR('V', 'A') (37) ( max { min | WA2(i)-WA3(j) | } + i j max { min | WA3(i)-WA2(j) | } ) / ( |D3| ulp ) i j ZSTEMR('N', 'A') vs. CSTEMR('V', 'A') The 'sizes' are specified by an array NN(1:NSIZES); the value of each element NN(j) specifies one size. The 'types' are specified by a logical array DOTYPE( 1:NTYPES ); if DOTYPE(j) is .TRUE., then matrix type 'j' will be generated. Currently, the list of possible types is: (1) The zero matrix. (2) The identity matrix. (3) A diagonal matrix with evenly spaced entries 1, ..., ULP and random signs. (ULP = (first number larger than 1) - 1 ) (4) A diagonal matrix with geometrically spaced entries 1, ..., ULP and random signs. (5) A diagonal matrix with 'clustered' entries 1, ULP, ..., ULP and random signs. (6) Same as (4), but multiplied by SQRT( overflow threshold ) (7) Same as (4), but multiplied by SQRT( underflow threshold ) (8) A matrix of the form U* D U, where U is unitary and D has evenly spaced entries 1, ..., ULP with random signs on the diagonal. (9) A matrix of the form U* D U, where U is unitary and D has geometrically spaced entries 1, ..., ULP with random signs on the diagonal. (10) A matrix of the form U* D U, where U is unitary and D has 'clustered' entries 1, ULP,..., ULP with random signs on the diagonal. (11) Same as (8), but multiplied by SQRT( overflow threshold ) (12) Same as (8), but multiplied by SQRT( underflow threshold ) (13) Hermitian matrix with random entries chosen from (-1,1). (14) Same as (13), but multiplied by SQRT( overflow threshold ) (15) Same as (13), but multiplied by SQRT( underflow threshold ) (16) Same as (8), but diagonal elements are all positive. (17) Same as (9), but diagonal elements are all positive. (18) Same as (10), but diagonal elements are all positive. (19) Same as (16), but multiplied by SQRT( overflow threshold ) (20) Same as (16), but multiplied by SQRT( underflow threshold ) (21) A diagonally dominant tridiagonal matrix with geometrically spaced diagonal entries 1, ..., ULP.

**Parameters***NSIZES*NSIZES is INTEGER The number of sizes of matrices to use. If it is zero, ZCHKST2STG does nothing. It must be at least zero.

*NN*NN is INTEGER array, dimension (NSIZES) An array containing the sizes to be used for the matrices. Zero values will be skipped. The values must be at least zero.

*NTYPES*NTYPES is INTEGER The number of elements in DOTYPE. If it is zero, ZCHKST2STG does nothing. It must be at least zero. If it is MAXTYP+1 and NSIZES is 1, then an additional type, MAXTYP+1 is defined, which is to use whatever matrix is in A. This is only useful if DOTYPE(1:MAXTYP) is .FALSE. and DOTYPE(MAXTYP+1) is .TRUE. .

*DOTYPE*DOTYPE is LOGICAL array, dimension (NTYPES) If DOTYPE(j) is .TRUE., then for each size in NN a matrix of that size and of type j will be generated. If NTYPES is smaller than the maximum number of types defined (PARAMETER MAXTYP), then types NTYPES+1 through MAXTYP will not be generated. If NTYPES is larger than MAXTYP, DOTYPE(MAXTYP+1) through DOTYPE(NTYPES) will be ignored.

*ISEED*ISEED is INTEGER array, dimension (4) On entry ISEED specifies the seed of the random number generator. The array elements should be between 0 and 4095; if not they will be reduced mod 4096. Also, ISEED(4) must be odd. The random number generator uses a linear congruential sequence limited to small integers, and so should produce machine independent random numbers. The values of ISEED are changed on exit, and can be used in the next call to ZCHKST2STG to continue the same random number sequence.

*THRESH*THRESH is DOUBLE PRECISION A test will count as 'failed' if the 'error', computed as described above, exceeds THRESH. Note that the error is scaled to be O(1), so THRESH should be a reasonably small multiple of 1, e.g., 10 or 100. In particular, it should not depend on the precision (single vs. double) or the size of the matrix. It must be at least zero.

*NOUNIT*NOUNIT is INTEGER The FORTRAN unit number for printing out error messages (e.g., if a routine returns IINFO not equal to 0.)

*A*A is COMPLEX*16 array of dimension ( LDA , max(NN) ) Used to hold the matrix whose eigenvalues are to be computed. On exit, A contains the last matrix actually used.

*LDA*LDA is INTEGER The leading dimension of A. It must be at least 1 and at least max( NN ).

*AP*AP is COMPLEX*16 array of dimension( max(NN)*max(NN+1)/2 ) The matrix A stored in packed format.

*SD*SD is DOUBLE PRECISION array of dimension( max(NN) ) The diagonal of the tridiagonal matrix computed by ZHETRD. On exit, SD and SE contain the tridiagonal form of the matrix in A.

*SE*SE is DOUBLE PRECISION array of dimension( max(NN) ) The off-diagonal of the tridiagonal matrix computed by ZHETRD. On exit, SD and SE contain the tridiagonal form of the matrix in A.

*D1*D1 is DOUBLE PRECISION array of dimension( max(NN) ) The eigenvalues of A, as computed by ZSTEQR simultaneously with Z. On exit, the eigenvalues in D1 correspond with the matrix in A.

*D2*D2 is DOUBLE PRECISION array of dimension( max(NN) ) The eigenvalues of A, as computed by ZSTEQR if Z is not computed. On exit, the eigenvalues in D2 correspond with the matrix in A.

*D3*D3 is DOUBLE PRECISION array of dimension( max(NN) ) The eigenvalues of A, as computed by DSTERF. On exit, the eigenvalues in D3 correspond with the matrix in A.

*D4*D4 is DOUBLE PRECISION array of dimension( max(NN) ) The eigenvalues of A, as computed by ZPTEQR(V). ZPTEQR factors S as Z4 D4 Z4* On exit, the eigenvalues in D4 correspond with the matrix in A.

*D5*D5 is DOUBLE PRECISION array of dimension( max(NN) ) The eigenvalues of A, as computed by ZPTEQR(N) when Z is not computed. On exit, the eigenvalues in D4 correspond with the matrix in A.

*WA1*WA1 is DOUBLE PRECISION array of dimension( max(NN) ) All eigenvalues of A, computed to high absolute accuracy, with different range options. as computed by DSTEBZ.

*WA2*WA2 is DOUBLE PRECISION array of dimension( max(NN) ) Selected eigenvalues of A, computed to high absolute accuracy, with different range options. as computed by DSTEBZ. Choose random values for IL and IU, and ask for the IL-th through IU-th eigenvalues.

*WA3*WA3 is DOUBLE PRECISION array of dimension( max(NN) ) Selected eigenvalues of A, computed to high absolute accuracy, with different range options. as computed by DSTEBZ. Determine the values VL and VU of the IL-th and IU-th eigenvalues and ask for all eigenvalues in this range.

*WR*WR is DOUBLE PRECISION array of dimension( max(NN) ) All eigenvalues of A, computed to high absolute accuracy, with different options. as computed by DSTEBZ.

*U*U is COMPLEX*16 array of dimension( LDU, max(NN) ). The unitary matrix computed by ZHETRD + ZUNGTR.

*LDU*LDU is INTEGER The leading dimension of U, Z, and V. It must be at least 1 and at least max( NN ).

*V*V is COMPLEX*16 array of dimension( LDU, max(NN) ). The Housholder vectors computed by ZHETRD in reducing A to tridiagonal form. The vectors computed with UPLO='U' are in the upper triangle, and the vectors computed with UPLO='L' are in the lower triangle. (As described in ZHETRD, the sub- and superdiagonal are not set to 1, although the true Householder vector has a 1 in that position. The routines that use V, such as ZUNGTR, set those entries to 1 before using them, and then restore them later.)

*VP*VP is COMPLEX*16 array of dimension( max(NN)*max(NN+1)/2 ) The matrix V stored in packed format.

*TAU*TAU is COMPLEX*16 array of dimension( max(NN) ) The Householder factors computed by ZHETRD in reducing A to tridiagonal form.

*Z*Z is COMPLEX*16 array of dimension( LDU, max(NN) ). The unitary matrix of eigenvectors computed by ZSTEQR, ZPTEQR, and ZSTEIN.

*WORK*WORK is COMPLEX*16 array of dimension( LWORK )

*LWORK*LWORK is INTEGER The number of entries in WORK. This must be at least 1 + 4 * Nmax + 2 * Nmax * lg Nmax + 3 * Nmax**2 where Nmax = max( NN(j), 2 ) and lg = log base 2.

*IWORK*IWORK is INTEGER array, Workspace.

*LIWORK*LIWORK is INTEGER The number of entries in IWORK. This must be at least 6 + 6*Nmax + 5 * Nmax * lg Nmax where Nmax = max( NN(j), 2 ) and lg = log base 2.

*RWORK*RWORK is DOUBLE PRECISION array

*LRWORK*LRWORK is INTEGER The number of entries in LRWORK (dimension( ??? )

*RESULT*RESULT is DOUBLE PRECISION array, dimension (26) The values computed by the tests described above. The values are currently limited to 1/ulp, to avoid overflow.

*INFO*INFO is INTEGER If 0, then everything ran OK. -1: NSIZES < 0 -2: Some NN(j) < 0 -3: NTYPES < 0 -5: THRESH < 0 -9: LDA < 1 or LDA < NMAX, where NMAX is max( NN(j) ). -23: LDU < 1 or LDU < NMAX. -29: LWORK too small. If ZLATMR, CLATMS, ZHETRD, ZUNGTR, ZSTEQR, DSTERF, or ZUNMC2 returns an error code, the absolute value of it is returned. ----------------------------------------------------------------------- Some Local Variables and Parameters: ---- ----- --------- --- ---------- ZERO, ONE Real 0 and 1. MAXTYP The number of types defined. NTEST The number of tests performed, or which can be performed so far, for the current matrix. NTESTT The total number of tests performed so far. NBLOCK Blocksize as returned by ENVIR. NMAX Largest value in NN. NMATS The number of matrices generated so far. NERRS The number of tests which have exceeded THRESH so far. COND, IMODE Values to be passed to the matrix generators. ANORM Norm of A; passed to matrix generators. OVFL, UNFL Overflow and underflow thresholds. ULP, ULPINV Finest relative precision and its inverse. RTOVFL, RTUNFL Square roots of the previous 2 values. The following four arrays decode JTYPE: KTYPE(j) The general type (1-10) for type 'j'. KMODE(j) The MODE value to be passed to the matrix generator for type 'j'. KMAGN(j) The order of magnitude ( O(1), O(overflow^(1/2) ), O(underflow^(1/2) )

**Author**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **620** of file **zchkst2stg.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page zchkst2stg(3) is an alias of zchkst2stg.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK