/ 
Test-Number-Delta-0.16
River stage three • 61 direct dependents • 312 total dependents
/ Test::Number::Delta

NAME

Test::Number::Delta - Compare if the difference between two numbers is within a specified amount

SYNOPSIS

# Default tolerance
use Test::Number::Delta;
delta_ok( 1e-5, 2e-5, 'values within 1e-6'); # not ok

# Specific tolerance for a single test
delta_within( 1e-3, 2e-3, 1e-4, 'values within 1e-4'); not ok

# Set a different default tolerance 
use Test::Number::Delta within => 1e-5;
delta_ok( 1e-5, 2e-5, 'values within 1e-5'); # ok

# Set a relative tolerance
use Test::Number::Delta relative => 1e-3;
delta_ok( 1.01, 1.0099, 'values within 1.01e-3'); # ok

DESCRIPTION

Most programmers at one time or another are confronted with the issue of comparing floating-point numbers for equality. The typical idiom is to test if the absolute value of the difference of the numbers is within a desired tolerance, usually called epsilon. This module provides such a function for use with Test::Harness. Usage is similar to other test functions described in Test::More. Semantically, the delta_within function replaces this kind of construct:

ok ( abs($p - $q) <= $epsilon, '$p is equal to $q' ) or
    diag "$p is not equal to $q to within $epsilon";

While there's nothing wrong with that construct, it's a pain to type it repeatedly in a test script. This module does the same thing with a single function call. The delta_ok function is similar, but either uses a global default value for epsilon so that it does not need to be specified repeatedly or else calculates a 'relative' epsilon on the fly so that epsilon is scaled automatically to the size of the arguments to delta_ok. Both functions are exported automatically.

USAGE

use Test::Number::Delta;

With no arguments, epsilon defaults to 1e-6. (An arbitrary choice on my part.)

use Test::Number::Delta within => 1e-9;

To specify a different default value for epsilon, provide a within parameter when importing the module.

use Test::Number::Delta relative => 1e-3;

As an alternative to using a fixed value for epsilon, provide a relative parameter when importing the module. This signals that delta_ok should test equality with an epsilon that is scaled to the size of the arguments. Epsilon is calculated as the relative value times the absolute value of the argument with the greatest magnitude. Mathematically, for arguments 'x' and 'y':

epsilon = relative * max( abs(x), abs(y) )

For example, a relative value of "0.01" would mean that the arguments are equal if they differ by no more than 1% of the larger of the two values. A relative value of 1e-6 means that the arguments must differ by no more than 1 millionth of the larger value.

Combining with a test plan

use Test::Number::Delta 'no_plan';

# or

use Test::Number::Delta within => 1e-9, tests => 1;

If a test plan has not already been specified, the optional parameter for Test::Number::Delta may be followed with a test plan (see Test::More for details). If a parameter for Test::Number::Delta is given, it must come first.

FUNCTIONS

delta_within

delta_within( $p, $q, $epsilon, '$p and $q are equal within $epsilon' );

This test compares equality within a given value of epsilon. The test is true if the absolute value of the difference between $p and $q is less than or equal to epsilon. If the test is true, it prints an "OK" statement for use in testing. If the test is not true, this function prints a failure report and diagnostic.

delta_ok

delta_ok( $p, $q, '$p and $q are close enough to equal' );

This test compares equality using one of two pre-set approaches for determining epsilon. (See "USAGE") If a within parameter was provided during use, that value is the default for epsilon. If a relative parameter was provided, that value is multiplied by the larger absolute value of the arguments to delta_ok to determine epsilon for that comparison. If neither parameter was specified, the default epsilon is 1e-6.

The test is true if the absolute value of the difference between $p and $q is less than or equal to epsilon. If the test is true, it prints an "OK" statement for use in testing. If the test is not true, this function prints a failure report and diagnostic.

BUGS

Please report bugs using the CPAN Request Tracker at http://rt.cpan.org/NoAuth/Bugs.html?Dist=Test-Number-Delta

AUTHOR

David A Golden <dagolden@cpan.org>

http://dagolden.com/

COPYRIGHT

Copyright (c) 2005 by David A. Golden

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.

SEE ALSO

Test::More, Test::Harness, Test::Builder