DCHKSB2STG(3)

📦 version 3.12.0, in opensuse-leap 16.0

💖 DCHKSB2STG(3) 💖

Okay bestie, this is the DCHKSB2STG(3) page from the Library Functions Manual, and the source file is:

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/EIG/dchksb2stg.f

✨ SYNOPSIS ✨

🧚 Functions/Subroutines 🧚

subroutine DCHKSB2STG (nsizes, nn, nwdths, kk, ntypes, dotype, iseed,
    thresh, nounit, a, lda, sd, se, d1, d2, d3, u, ldu, work, lwork,
    result, info)
    DCHKSB2STG

🔥 Function/Subroutine Documentation 🔥

Here’s the full signature, character for character:

subroutine DCHKSB2STG (integer nsizes, integer, dimension( * ) nn, integer
    nwdths, integer, dimension( * ) kk, integer ntypes, logical, dimension(
    * ) dotype, integer, dimension( 4 ) iseed, double precision thresh,
    integer nounit, double precision, dimension( lda, * ) a, integer lda,
    double precision, dimension( * ) sd, double precision, dimension( * )
    se, double precision, dimension( * ) d1, double precision, dimension( *
    ) d2, double precision, dimension( * ) d3, double precision, dimension(
    ldu, * ) u, integer ldu, double precision, dimension( * ) work, integer
    lwork, double precision, dimension( * ) result, integer info)
    DCHKSB2STG

🌸 Purpose 🌸

No cap, DCHKSB2STG tests the reduction of a symmetric band matrix to tridiagonal form, used with the symmetric eigenvalue problem.

DSBTRD factors a symmetric band matrix A as U S U', where ' means transpose, S is symmetric tridiagonal, and U is orthogonal. DSBTRD can use either just the lower or just the upper triangle of A; DCHKSB2STG checks both cases.

DSYTRD_SB2ST factors a symmetric band matrix A as U S U', where ' means transpose, S is symmetric tridiagonal, and U is orthogonal. DSYTRD_SB2ST can use either just the lower or just the upper triangle of A; DCHKSB2STG checks both cases.

DSTEQR factors S as Z D1 Z'.

D1 is the matrix of eigenvalues computed when Z is not computed and from the S resulting of DSBTRD (used as reference for DSYTRD_SB2ST).

D2 is the matrix of eigenvalues computed when Z is not computed and from the S resulting of DSYTRD_SB2ST.

D3 is the matrix of eigenvalues computed when Z is not computed and from the S resulting of DSYTRD_SB2ST.

When DCHKSB2STG is called, a number of matrix sizes (), a number of bandwidths (), and a number of matrix types () are specified. For each size (), each bandwidth () less than or equal to ___, and each type of matrix, one matrix will be generated and used to test the symmetric banded reduction routine. For each matrix, a number of tests will be performed:

  • (1) | A - V S V' | / ( |A| n ulp ) computed by DSBTRD with UPLO='U'
  • (2) | I - UU' | / ( n ulp )
  • (3) | A - V S V' | / ( |A| n ulp ) computed by DSBTRD with UPLO='L'
  • (4) | I - UU' | / ( n ulp )
  • (5) | D1 - D2 | / ( |D1| ulp ) where D1 is computed by DSBTRD with UPLO='U' and D2 is computed by DSYTRD_SB2ST with UPLO='U'
  • (6) | D1 - D3 | / ( |D1| ulp ) where D1 is computed by DSBTRD with UPLO='U' and D3 is computed by DSYTRD_SB2ST with UPLO='L'

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 ___ 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 orthogonal 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 orthogonal 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 orthogonal and D has ___ 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) Symmetric 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 )

🎀 Parameters 🎀

  • NSIZES — INTEGER. The number of sizes of matrices to use. If it is zero, DCHKSB2STG does nothing. It must be at least zero.
  • NN — 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.
  • NWDTHS — INTEGER. The number of bandwidths to use. If it is zero, DCHKSB2STG does nothing. It must be at least zero.
  • KK — INTEGER array, dimension (NWDTHS). An array containing the bandwidths to be used for the band matrices. The values must be at least zero.
  • NTYPES — INTEGER. The number of elements in DOTYPE. If it is zero, DCHKSB2STG 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 — 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 — 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 DCHKSB2STG to continue the same random number sequence.
  • THRESH — DOUBLE PRECISION. A test will count as a fail if the computed value (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 — INTEGER. The FORTRAN unit number for printing out error messages (e.g., if a routine returns IINFO not equal to 0.)
  • A — DOUBLE PRECISION array, dimension (LDA, max(NN)). Used to hold the matrix whose eigenvalues are to be computed.
  • LDA — INTEGER. The leading dimension of A. It must be at least 2 (not 1!) and at least max( KK )+1.
Bestie, seriously: not 1. The page says “not 1!” and it means it.
  • SD — DOUBLE PRECISION array, dimension (max(NN)). Used to hold the diagonal of the tridiagonal matrix computed by DSBTRD.
  • SE — DOUBLE PRECISION array, dimension (max(NN)). Used to hold the off-diagonal of the tridiagonal matrix computed by DSBTRD.
  • D1 — DOUBLE PRECISION array, dimension (max(NN)).
  • D2 — DOUBLE PRECISION array, dimension (max(NN)).
  • D3 — DOUBLE PRECISION array, dimension (max(NN)).
  • U — DOUBLE PRECISION array, dimension (LDU, max(NN)). Used to hold the orthogonal matrix computed by DSBTRD.
  • LDU — INTEGER. The leading dimension of U. It must be at least 1 and at least max( NN ).
  • WORK — DOUBLE PRECISION array, dimension (LWORK).
  • LWORK — INTEGER. The number of entries in WORK. This must be at least max( LDA+1, max(NN)+1 )*max(NN).
  • RESULT — DOUBLE PRECISION array, dimension (4). The values computed by the tests described above. The values are currently limited to 1/ulp, to avoid overflow.
  • INFO — the page part 1 ends right at the INFO label; the rest of INFO is in part 2 💖

Okay so picking up right here: INFO is INTEGER. If it’s 0, then everything ran OK — no cap, that’s the good ending. ✅💖

Some Local Variables and Parameters 🧚

Yes bestie, these are the little guys doing the work:

  • 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.
  • 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: (yes, the source says four — we report, we don’t edit 💅)

  • KTYPE(j) — The general type (1-10) for type .
  • KMODE(j) — The MODE value to be passed to the matrix generator for type .
  • 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 329 of file dchksb2stg.f.

Author ✨ (the meta one)

Generated automatically by Doxygen for LAPACK from the source code.

That’s the tea, bestie: source file /home/abui...chksb2stg.f, version LAPACK 3.12.0 🌈 — and the footer didn’t hand us a date, so we’re not inventing one, periodt. 🎀✨

📦 where this page comes from