TESTING/EIG/dchksb.f(3)

💖 NAME 💖

This is TESTING/EIG/dchksb.f(3) from the Library Functions Manual, bestie — manual name TESTING/EIG/dchksb.f. It's the page for the DCHKSB subroutine, and it's giving “backstage pass to the symmetric band reduction test suite” energy. 🦋

✨ SYNOPSIS ✨

🎀 Functions/Subroutines 🎀

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

DCHKSB

🌟 Function/Subroutine Documentation 🌟

subroutine dchksb (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( ldu, * ) u, integer ldu, double
    precision, dimension( * ) work, integer lwork, double precision,
    dimension( * ) result, integer info)

DCHKSB

💅 Purpose 💅

Okay so DCHKSB tests the reduction of a symmetric band matrix to tridiagonal form, used with the symmetric eigenvalue problem. Periodt.

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; DCHKSB checks both cases. No cap.

When DCHKSB is called, a number of matrix … (()), a number of bandwidths …, and a number of matrix … 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 )

The … are specified by an array NN(1:NSIZES); the value of each element NN(j) specifies one size.

The … are specified by a logical array DOTYPE( 1:NTYPES ); if DOTYPE(j) is .TRUE., then matrix type … 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 — NSIZES is INTEGER. The number of sizes of matrices to use. If it is zero, DCHKSB 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.
• NWDTHS — NWDTHS is INTEGER. The number of bandwidths to use. If it is zero, DCHKSB does nothing. It must be at least zero.
• KK — KK is INTEGER array, dimension (NWDTHS). An array containing the bandwidths to be used for the band matrices. The values must be at least zero.
• NTYPES — NTYPES is INTEGER. The number of elements in DOTYPE. If it is zero, DCHKSB 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 DCHKSB to continue the same random number sequence.
• THRESH — THRESH is DOUBLE PRECISION. A test will count as … if the …, 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 DOUBLE PRECISION array, dimension (LDA, max(NN)). Used to hold the matrix whose eigenvalues are to be computed.
• LDA — LDA is INTEGER. The leading dimension of A. It must be at least 2 (not 1!) and at least max( KK )+1.
• SD — SD is DOUBLE PRECISION array, dimension (max(NN)). Used to hold the diagonal of the tridiagonal matrix computed by DSBTRD.
• SE — SE is DOUBLE PRECISION array, dimension (max(NN)). Used to hold the off-diagonal of the tridiagonal matrix computed by DSBTRD.
• U — U is DOUBLE PRECISION array, dimension (LDU, max(NN)). Used to hold the orthogonal matrix computed by DSBTRD.
• LDU — LDU is INTEGER. The leading dimension of U. It must be at least 1 and at least max( NN ).
• WORK — WORK is DOUBLE PRECISION array, dimension (LWORK).
• LWORK — LWORK is INTEGER. The number of entries in WORK. This must be at least max( LDA+1, max(NN)+1 )*max(NN).
• RESULT — RESULT is 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 — INFO is INTEGER. If 0, then everything ran OK.

🌸 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.
• 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 ….
  • 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 290 of file dchksb.f.

👑 Author 👑

Generated automatically by Doxygen for LAPACK from the source code.

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That's the whole page, bestie. Source/version vibe: LAPACK Version 3.12.0, for TESTING/EIG/dchksb.f(3). The original footer didn't hand me a date, so I'm not inventing one — no cap. 💜