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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 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 949951
              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  pur-poses. purposes.
                     poses.  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 cre-ate create
              ate 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 cal-culators calculators
                     culators 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.


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




math                                                 1.0                         tclrep/machineparameters(n)