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Math::SigFigs - do math with correct handling of significant figures

• NAME
• SYNOPSIS
• DESCRIPTION
• ROUTINES
• KNOWN PROBLEMS
• AUTHOR

NAME

Math::SigFigs - do math with correct handling of significant figures

SYNOPSIS

If you only need to use CountSigFigs and FormatSigFigs, use the first form. If you are going to be doing arithmetic, use the second line.

  use Math::SigFigs;
  use Math::SigFigs qw(:all);

The following routines do simple counting/formatting:

  $n=CountSigFigs($num);
  $num=FormatSigFigs($num,$n);

Use the following routines to do arithmetic operations.

  $num=addSF($n1,$n2);
  $num=subSF($n1,$n2);
  $num=multSF($n1,$n2);
  $num=divSF($n1,$n2);

DESCRIPTION

In many scientific applications, it is often useful to be able to format numbers with a given number of significant figures, or to do math in such a way as to maintain the correct number of significant figures. The rules for significant figures are too complicated to be handled solely using the sprintf function (unless you happen to be Randal Schwartz :-).

These routines allow you to correctly handle significan figures.

It can count the number of significan figures, format a number to a given number of significant figures, and do basic arithmetic.

ROUTINES

CountSigFigs

  $n=CountSigFigs($N);

This returns the number of significant figures in a number. It returns () if $N is not a number.

  $N      $n
  -----   --
  240     2
  240.    3
  241     3
  0240    2
  0.03    1
  0       0
  0.0     0

FormatSigFigs

  $str=FormatSigFigs($N,$n)

This returns a string containing $N formatted to $n significant figures. This will work for all cases except something like ``2400'' formatted to 3 significant figures.

  $N     $n   $str
  ------ --   -------
  2400    1   2000
  2400    2   2400
  2400    3   2400
  2400    4   2400.
  2400    5   2400.0

  141     3   141.
  141     2   140

  0.039   1   0.04
  0.039   2   0.039

  9.9     1   10
  9.9     2   9.9
  9.9     3   9.90

addSF, subSF, multSF, divSF

These routines add/subtract/multiply/divide two numbers while maintaining the proper number of significant figures.

KNOWN PROBLEMS

Without scientific notation, some numbers are ambiguous

These routines do not work with scientific notation (exponents). As a result, it is impossible to unambiguously format some numbers. For example,

  $str=FormatSigFigs("2400",3);

will by necessity return the string ``2400'' which does NOT have 3 significant figures. This is not a bug. It is simply a fundamental problem with working with significant figures when not using scientific notation.

A bug in some printf library calls on the Mac

One of the tests

   FormatSigFigs(0.99,1)  =>  1.

fails on at least some Mac OS versions. It gives ``0.'' instead of ``1.'' and comes when the call:

   printf("%.0f","0.99")

returns 0 instead of 1. I have not added a workaround for this.

AUTHOR

Sullivan Beck (sbeck@cpan.org)

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