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math::machineparameters - Compute double precision machine parameters.

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package require Tcl 8.4
package require snit
package require math::machineparameters 0.1

machineparameters create objectname ?options...?
objectname configure ?options...?
objectname cget opt
objectname destroy
objectname compute
objectname get key
objectname tostring
objectname print


The math::machineparameters package is the Tcl equivalent of the DLAMCH LAPACK function. In floating point systems, a floating point number is represented by

x = +/- d1 d2 ... dt basis^e

where digits satisfy

0 <= di <= basis - 1, i = 1, t

with the convention :

The compute method computes all machine parameters. Then, the get method can be used to get each parameter. The print method prints a report on standard output.


In the following example, one compute the parameters of a desktop under Linux with the following Tcl 8.4.19 properties :

% parray tcl_platform
tcl_platform(byteOrder) = littleEndian
tcl_platform(machine)   = i686
tcl_platform(os)        = Linux
tcl_platform(osVersion) = 2.6.24-19-generic
tcl_platform(platform)  = unix
tcl_platform(tip,268)   = 1
tcl_platform(tip,280)   = 1
tcl_platform(user)      = <username>
tcl_platform(wordSize)  = 4

The following example creates a machineparameters object, computes the properties and displays it.

set pp [machineparameters create %AUTO%]
$pp compute
$pp print
$pp destroy

This prints out :

Machine parameters
Epsilon : 1.11022302463e-16
Beta : 2
Rounding : proper
Mantissa : 53
Maximum exponent : 1024
Minimum exponent : -1021
Overflow threshold : 8.98846567431e+307
Underflow threshold : 2.22507385851e-308

That compares well with the results produced by Lapack 3.1.1 :

Epsilon                      =   1.11022302462515654E-016
Safe minimum                 =   2.22507385850720138E-308
Base                         =    2.0000000000000000
Precision                    =   2.22044604925031308E-016
Number of digits in mantissa =    53.000000000000000
Rounding mode                =   1.00000000000000000
Minimum exponent             =   -1021.0000000000000
Underflow threshold          =   2.22507385850720138E-308
Largest exponent             =    1024.0000000000000
Overflow threshold           =   1.79769313486231571E+308
Reciprocal of safe minimum   =   4.49423283715578977E+307

The following example creates a machineparameters object, computes the properties and gets the epsilon for the machine.

set pp [machineparameters create %AUTO%]
$pp compute
set eps [$pp get -epsilon]
$pp destroy




Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category math of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.


Copyright © 2008 Michael Baudin