tclrep/machineparameters(n)					      tclrep					       tclrep/machineparameters(n)

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NAME

       tclrep/machineparameters - Compute double precision machine parameters.

SYNOPSIS

       package require snit

       machineparameters create objectname ?options...?

       objectname configure ?options...?

       objectname cget opt

       objectname destroy

       objectname compute

       objectname get key

       objectname tostring

       objectname print

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DESCRIPTION

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

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

       where digits satisfy

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

       with the convention :

       o      t is the size of the mantissa

       o      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

       o      "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

       o      "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.

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

	      o      -rounding : The rounding mode used on the machine.  The rounding occurs when more than t digits would be required	to  repre-
		     sent  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".

	      o      -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...

	      o      -mantissa : the number of bits in the mantissa

	      o      -exponentmax :  the largest positive exponent before overflow occurs

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

	      o      -vmax : largest positive value before overflow occurs

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

       objectname tostring
	      Return a report for machine parameters.

       objectname print
	      Print machine parameters on standard output.

COPYRIGHT

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

math									1.0					       tclrep/machineparameters(n)