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tclrep/machineparameters(3tcl) tclrep tclrep/machineparameters(3tcl)
 


NAME

tclrep/machineparameters - Compute double precision machine parameters.

SYNOPSIS

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





 


DESCRIPTION

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 :


  
•

  
t is the size of the mantissa





  
•

  
basis is the basis (the "radix")





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.

EXAMPLE

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







REFERENCES



  
•

  
"Algorithms to Reveal Properties of Floating-Point Arithmetic",
      Michael A. Malcolm, Stanford University, Communications of the ACM, Volume
      15 , Issue 11 (November 1972), Pages: 949 - 951





  
•

  
"More on Algorithms that Reveal Properties of Floating, Point
      Arithmetic Units", W. Morven Gentleman, University of Waterloo, Scott
      B. Marovich, Purdue University, Communications of the ACM, Volume 17 ,
      Issue 5 (May 1974), Pages: 276 - 277




CLASS API



  
machineparameters create objectname ?options...?

  
The command creates a new machineparameters object and returns the fully
      qualified name of the object command as its result.







  
-verbose verbose

  
Set this option to 1 to enable verbose logging. This option is mainly for
      debug purposes. The default value of verbose is 0.






OBJECT API



  
objectname configure ?options...?

  
The command configure the options of the object objectname. The
      options are the same as the static method create.





  
objectname cget opt

  
Returns the value of the option which name is opt. The options are
      the same as the method create and configure.





  
objectname destroy

  
Destroys the object objectname.





  
objectname compute

  
Computes the machine parameters.





  
objectname get key

  
Returns the value corresponding with given key. The following is the list
      of available keys.







  
•

  
-epsilon : smallest value so that 1+epsilon>1 is false





  
•

  
-rounding : The rounding mode used on the machine. The rounding occurs
      when more than t digits would be required to represent the number. Two
      modes can be determined with the current system : "chop" means
      than only t digits are kept, no matter the value of the number
      "proper" means that another rounding mode is used, be it
      "round to nearest", "round up", "round
      down".





  
•

  
-basis : the basis of the floating-point representation. The basis is
      usually 2, i.e. binary representation (for example IEEE 754 machines), but
      some machines (like HP calculators for example) uses 10, or 16,
    etc...





  
•

  
-mantissa : the number of bits in the mantissa





  
•

  
-exponentmax : the largest positive exponent before overflow occurs





  
•

  
-exponentmin : the largest negative exponent before (gradual) underflow
      occurs





  
•

  
-vmax : largest positive value before overflow occurs





  
•

  
-vmin : largest negative value before (gradual) underflow occurs







  
objectname tostring

  
Return a report for machine parameters.





  
objectname print

  
Print machine parameters on standard output.




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 [http://core.tcl.tk/tcllib/reportlist]. Please also
  report any ideas for enhancements you may have for either package and/or
  documentation.

COPYRIGHT


Copyright (c) 2008 Michael Baudin <michael.baudin@sourceforge.net>








  

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