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Test::Number::Delta - Compare the difference between numbers against a given tolerance
# Import test functions use Test::Number::Delta; # Equality test with default tolerance delta_ok( 1e-5, 2e-5, 'values within 1e-6'); # Inequality test with default tolerance delta_not_ok( 1e-5, 2e-5, 'values not within 1e-6'); # Provide specific tolerance delta_within( 1e-3, 2e-3, 1e-4, 'values within 1e-4'); delta_not_within( 1e-3, 2e-3, 1e-4, 'values not within 1e-4'); # Compare arrays or matrices @a = ( 3.14, 1.41 ); @b = ( 3.15, 1.41 ); delta_ok( \@a, \@b, 'compare @a and @b' ); # Set a different default tolerance use Test::Number::Delta within => 1e-5; delta_ok( 1.1e-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');
At some point or another, most programmers find they need to compare 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 painful 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 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.
Because checking floating-point equality is not always reliable, it is not possible to check the 'equal to' boundary of 'less than or equal to epsilon'. Therefore, Test::Number::Delta only compares if the absolute value of the difference is less than epsilon (for equality tests) or greater than epsilon (for inequality tests).
With no arguments, epsilon defaults to 1e-6. (An arbitrary choice on the author's part.)
To specify a different default value for epsilon, provide a
within parameter when importing the module. The value must be non-zero.
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 less than 1% of the larger of the two values. A relative value of 1e-6 means that the arguments must differ by less than 1 millionth of the larger value. The relative value must be non-zero.
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.
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 function tests for 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 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. Epsilon must be non-zero.
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_within( \@a, \@b, 1e-6, 'compare @a and @b' );
The sample prints the following:
not ok 1 - compare @a and @b # At : 1.4100000 and 1.4200000 are not equal to within 0.000001
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 function tests for equality within a default epsilon value. See "USAGE" for details on changing the default. Otherwise, this function works the same as
delta_not_within( $p, $q, '$p and $q are different' ); delta_not_within( \@p, \@q, $epsilon, '@p and @q are different' );
This test compares inequality in excess of a given value of epsilon. The test is true if the absolute value of the difference between $p and $q is greater than epsilon. For array or matrix comparisons, the test is true if any pair of values differs by more than epsilon. Otherwise, this function works the same as
delta_not_ok( $p, $q, '$p and $q are different' ); delta_not_ok( \@p, \@q, '@p and @q are different' );
This function tests for inequality in excess of a default epsilon value. See "USAGE" for details on changing the default. Otherwise, this function works the same as
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 http://rt.cpan.org/Dist/Display.html?Queue=Test-Number-Delta
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.
David A Golden (DAGOLDEN)
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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