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 useful (and in some cases
required) 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.
These routines allow you to correctly handle significant figures. It can
handle real number or exponentials correctly.
It can count the number of significant figures, format a number to a
given number of significant figures, and do basic arithmetic.
ROUTINES
All routines return nothing if something other than a valid number is
passed in for any argument.
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
0.030 2
1.2e2 2
The number zero is not as well defined as other numbers. I have seen
different answers for this. I have seen answers that say that '0'
has 0, 1, or infinite significant figures and for '0.00', I have
seen the number of significant figures given as 0, 1, 2, and 3.
Everyone agrees on how to count signficant figures for non-zero
numbers... but that agreement doesn't hold true for zero. At this
time, this module will return:
$N $n
----- --
0 1
0.0 1
0.00 2
0.0e2 1
I may try to improve the handling of zero at some point.
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
0.0300 2 0.030
9.9 1 10
9.9 2 9.9
9.9 3 9.90
0 2 0.00
addSF, subSF, multSF, divSF
These routines add/subtract/multiply/divide two numbers while
maintaining the proper number of significant figures.
Working with zero is a special case. If 0 has 1 signficiant figure
(i.e. '0') it is treated as exact. If it has more significant
figures (i.e. 0.00), that number is used as appropriate.
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.
The number zero is ambiguous
There is not a universally accepted way to specify the number of
significant figures that the number 0 has.
perl cannot preserve significant figures in numbers
If you run:
CountSigFigs(20.00);
=> 1
CountSigFigs("20.00");
=> 4
This is simply due to the way that numbers are stored. When using
this module, use numbers stored as strings in order to avoid
unexpected results.
LICENSE
This script is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
AUTHOR
Sullivan Beck (sbeck@cpan.org)