math::machineparameters(3tcl) tclrep math::machineparameters(3tcl) 







math::machineparameters - Compute double precision machine
    parameters.








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



















  

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







  

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













  

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

  

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

  

  
Destroys the object objectname.

  

  
Computes the machine parameters.

  

  
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
    • 






  

  
Return a report for machine parameters.

  

  
Print machine parameters on standard output.










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.


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








  

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