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 # Compare arrays or matrices @a = ( 3.14, 1.41 ); @b = ( 3.15, 1.41 ); delta_ok( \@a, \@b, 'compare @a and @b' ); 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' ); 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. The values to compare may be scalars or references to arrays. If the values are references to arrays, the comparison is done pairwise for each index value of the array. The pairwise comparison is recursive, so matrices may be compared as well. For example, this code sample compares two matrices: my @a = ( [ 3.14, 6.28 ], [ 1.41, 2.84 ] ); my @b = ( [ 3.14, 6.28 ], [ 1.42, 2.84 ] ); delta_ok( \@a, \@b, 'compare @a and @b' ); The sample prints the following: not ok 1 - compare @a and @b # At [1][0]: 1.4100000 and 1.4200000 are not equal to within 0.000001 delta_ok delta_ok( $p, $q, '$p and $q are close enough to equal' ); 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. As with "delta_within", the values to compare may be scalars or references to arrays. SEE ALSO Test::More, Test::Harness, Test::Builder BUGS Please report any bugs or feature using the CPAN Request Tracker. Bugs can be submitted by email to "bug-Test-Number-Delta@rt.cpan.org" or through the web interface at When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature. AUTHOR David A Golden (DAGOLDEN) dagolden@cpan.org COPYRIGHT Copyright (c) 2005, 2006 by David A. Golden This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. 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