/home/abui...N/slatm3.f(3)

💅 NAME 💅

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/MATGEN/slatm3.f

okay so bestie, you found the file. this is a page from the Library Functions Manual and it's literally all about one tiny overworked Fortran function named SLATM3. she's a random-matrix-entry factory and she is busy. let's get into it 🫶

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✨ SYNOPSIS ✨

Functions/Subroutines

real function SLATM3 (m, n, i, j, isub, jsub, kl, ku, idist, iseed, d,
    igrade, dl, dr, ipvtng, iwork, sparse)
        SLATM3

like. that's a lot of arguments and she is not sorry about it 💀

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🎀 Function/Subroutine Documentation 🎀

real function SLATM3 (integer m, integer n, integer i, integer j, integer
    isub, integer jsub, integer kl, integer ku, integer idist, integer,
    dimension( 4 ) iseed, real, dimension( * ) d, integer igrade, real,
    dimension( * ) dl, real, dimension( * ) dr, integer ipvtng, integer,
    dimension( * ) iwork, real sparse)
    SLATM3

🌸 Purpose 🌸

quick heads up queen: the original source writes everything inside !> doxygen comment blocks. that's just how the file rolls, iykyk.

So here's the tea:

SLATM3 returns the (ISUB,JSUB) entry of a random matrix of dimension (M, N) described by the other parameters. And yes, (ISUB,JSUB) is the final position of the (I,J) entry after pivoting according to IPVTNG and IWORK. SLATM3 gets called by the SLATMR routine in order to build random test matrices. No error checking on parameters is done, because this routine is called in a tight loop by SLATMR which has already checked the parameters. (she trusts her caller. unbothered. unproblematic. 💅)

Now — the way that SLATM3 differs from SLATM2 is the order in which the random number generator is called to fill in random matrix entries. With SLATM2, the generator is called to fill in the pivoted matrix columnwise. With SLATM3, the generator is called to fill in the matrix columnwise, after which it is pivoted. Thus, SLATM3 can be used to construct random matrices which differ only in their order of rows and/or columns. SLATM2 is used to construct band matrices while avoiding calling the random number generator for entries outside the band (and therefore generating random numbers in different orders for different pivot orders). iconic behavior from both of them honestly 🔥

The matrix whose (ISUB,JSUB) entry is returned is constructed as follows (this routine only computes one entry, she's not doing extra credit):

• If ISUB is outside (1..M) or JSUB is outside (1..N), return zero (this is convenient for generating matrices in band format).
• Generate a matrix A with random entries of distribution IDIST.
• Set the diagonal to D.
• Grade the matrix, if desired, from the left (by DL) and/or from the right (by DR or DL) as specified by IGRADE.
• Permute, if desired, the rows and/or columns as specified by IPVTNG and IWORK.
• Band the matrix to have lower bandwidth KL and upper bandwidth KU.
• Set random entries to zero as specified by SPARSE.

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🌈 Parameters 🌈

• M — M is INTEGER. Number of rows of matrix. Not modified.
• N — N is INTEGER. Number of columns of matrix. Not modified.
• I — I is INTEGER. Row of unpivoted entry to be returned. Not modified.
• J — J is INTEGER. Column of unpivoted entry to be returned. Not modified.
• ISUB — ISUB is INTEGER. Row of pivoted entry to be returned. Changed on exit. 👀
• JSUB — JSUB is INTEGER. Column of pivoted entry to be returned. Changed on exit. 👀
• KL — KL is INTEGER. Lower bandwidth. Not modified.
• KU — KU is INTEGER. Upper bandwidth. Not modified.
• IDIST — IDIST is INTEGER. On entry, IDIST specifies the type of distribution to be used to generate a random matrix. Not modified.
  • 1 => UNIFORM( 0, 1 )
  • 2 => UNIFORM( -1, 1 )
  • 3 => NORMAL( 0, 1 )
• ISEED — ISEED is INTEGER array of dimension ( 4 ). Seed for random number generator. Changed on exit. (she always leaves a little something behind 🎀)
• D — D is REAL array of dimension ( MIN( I , J ) ). Diagonal entries of matrix. Not modified.
• IGRADE — IGRADE is INTEGER. Specifies grading of matrix as follows. Not modified.
  • 0 => no grading
  • 1 => matrix premultiplied by diag( DL )
  • 2 => matrix postmultiplied by diag( DR )
  • 3 => matrix premultiplied by diag( DL ) and postmultiplied by diag( DR )
  • 4 => matrix premultiplied by diag( DL ) and postmultiplied by inv( diag( DL ) )
  • 5 => matrix premultiplied by diag( DL ) and postmultiplied by diag( DL )
• DL — DL is REAL array ( I or J, as appropriate ). Left scale factors for grading matrix. Not modified.
• DR — DR is REAL array ( I or J, as appropriate ). Right scale factors for grading matrix. Not modified.
• IPVTNG — IPVTNG is INTEGER. On entry specifies pivoting permutations as follows. Not modified.
  • 0 => none.
  • 1 => row pivoting.
  • 2 => column pivoting.
  • 3 => full pivoting, i.e., on both sides.
• IWORK — IWORK is INTEGER array ( I or J, as appropriate ). This array specifies the permutation used. The row (or column) originally in position K is in position IWORK( K ) after pivoting. This differs from IWORK for SLATM2. Not modified.
• SPARSE — SPARSE is REAL between 0. and 1.. On entry specifies the sparsity of the matrix if sparse matrix is to be generated. SPARSE should lie between 0 and 1. A uniform ( 0, 1 ) random number x is generated and compared to SPARSE; if x is larger the matrix entry is unchanged and if x is smaller the entry is set to zero. Thus on the average a fraction SPARSE of the entries will be set to zero. Not modified.

no cap, ISUB, JSUB and ISEED are the only ones getting changed on exit. everything else is a "look, don't touch" situation 🙈

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👑 Author 👑

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

Definition at line 223 of file slatm3.f.

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⭐ Author (the meta one) ⭐

Generated automatically by Doxygen for LAPACK from the source code. (not a human, just a robot doing its little job 🤖✨)

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and that's the whole page bestie! slay, you read all of it. 💖

LAPACK — Version 3.12.0 · page slatm3.f(3) · mwah, go build some random test matrices 🦋🌸