


math::constants(n)       Tcl Math Library      math::constants(n)


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NAME
       math::constants - Mathematical and numerical constants

SYNOPSIS
       package require Tcl  ?8.3?

       package require math::constants  ?1.0.1?

       ::math::constants::constants args

       ::math::constants::print-constants args

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DESCRIPTION
       This  package defines some common mathematical and numerical constants.
       By using the package you get consistent values for numbers like pi  and
       ln(10).

       It defines two commands:

       o      One for importing the constants

       o      One  for  reporting  which constants are defined and what values
              they actually have.


       The motivation for this package is that quite often,  with  (mathemati-
       cal)  computations, you need a good approximation to, say, the ratio of
       degrees to radians. You can, of course, define this like:

           variable radtodeg [expr {180.0/(4.0*atan(1.0))}]

       and use the variable radtodeg whenever you need the conversion.

       This has two drawbacks:

       o      You need to remember the proper formula or  value  and  that  is
              error-prone.

       o      Especially  with the use of mathematical functions like atan you
              assume that they have been accurately implemented. This is  sel-
              dom  or  never the case and for each platform you can get subtle
              differences.

       Here is the way you can do it with the math::constants package:

           package require math::constants
           ::math::constants::constants radtodeg degtorad

       which creates two variables, radtodeg and (its reciprocal) degtorad  in
       the calling namespace.



math                          1.0.1                             1





math::constants(n)       Tcl Math Library      math::constants(n)


       Constants  that  have  been defined (their values are mostly taken from
       mathematical tables with more precision than usually  can  be  handled)
       include:

       o      basic constants like pi, e, gamma (Euler's constant)

       o      derived values like ln(10) and sqrt(2)

       o      purely numerical values such as 1/3 that are included for conve-
              nience and for the fact that certain seemingly trivial  computa-
              tions like:

                  set value [expr {3.0*$onethird}]

              give  exactly the value you expect (if IEEE arithmetic is avail-
              able).


PROCEDURES
       The package defines the following public procedures:

       ::math::constants::constants args
              Import the constants whose names are given as arguments


       ::math::constants::print-constants args
              Print the constants whose names are given as  arguments  on  the
              screen  (name,  value  and  description) or, if no arguments are
              given, print all defined constants. This is mainly a convenience
              procedure.


BUGS, IDEAS, FEEDBACK
       This  document,  and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the  category  math  ::
       constants     of     the    Tcllib    SF    Trackers    [http://source-
       forge.net/tracker/?group_id=12883].  Please also report any  ideas  for
       enhancements you may have for either package and/or documentation.

KEYWORDS
       constants, degrees, e, math, pi, radians

CATEGORY
       Mathematics

COPYRIGHT
       Copyright (c) 2004 Arjen Markus <arjenmarkus@users.sourceforge.net>










math                          1.0.1                             2


