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Man Pages


Manual Reference Pages  -  MATH::UTILS (3)

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NAME

Math::Utils - Useful mathematical functions not in Perl.

CONTENTS

SYNOPSIS



    use Math::Utils qw(:utility);    # Useful functions

    #
    # Base 10 and base 2 logarithms.
    #
    $scale = log10($pagewidth);
    $bits = log2(1/$probability);

    #
    # Two uses of sign().
    #
    $d = sign($z - $w);

    @ternaries = sign(@coefficients);

    #
    # Using copysign(), $dist will be doubled negative or
    # positive $offest, depending upon whether ($from - $to)
    # is positive or negative.
    #
    my $dist = copysign(2 * $offset, $from - $to);

    #
    # Change increment direction if goal is negative.
    #
    $incr = flipsign($incr, $goal);

    #
    # floor() and ceil() functions.
    #
    $point = floor($goal);
    $limit = ceil($goal);

    #
    # The remainders of n after successive divisions of b, or
    # remainders after a set of divisions.
    #
    @rems = moduli($n, $b);



or



    use Math::Utils qw(:compare);    # Make comparison functions with tolerance.

    #
    # Floating point comparison function.
    #
    my $fltcmp = generate_fltmcp(1.0e-7);

    if (&$fltcmp($x0, $x1) < 0)
    {
        add_left($data);
    }
    else
    {
        add_right($data);
    }

    #
    # Or we can create single-operation comparison functions.
    #
    # Here we are only interested in the greater than and less than
    # comparison functions.
    #
    my(undef, undef,
        $approx_gt, undef, $approx_lt) = generate_relational(1.5e-5);



or



    use Math::Utils qw(:polynomial);    # Basic polynomial ops

    #
    # Coefficient lists run from 0th degree upward, left to right.
    #
    my @c1 = (1, 3, 5, 7, 11, 13, 17, 19);
    my @c2 = (1, 3, 1, 7);
    my @c3 = (1, -1, 1)

    my $c_ref = pl_mult(\@c1, \@c2);
    $c_ref = pl_add($c_ref, \@c3);



EXPORT

All functions can be exported by name, or by using the tag that they’re grouped under.

    utility tag

Useful, general-purpose functions, including those that originated in FORTRAN and were implemented in Perl in the module Math::Fortran, by J. A. R. Williams.

There is a name change — copysign() was known as sign() in Math::Fortran.

log10()



    $xlog10 = log10($x);
    @xlog10 = log10(@x);



Return the log base ten of the argument. A list form of the function is also provided.

log2()



    $xlog2 = log2($x);
    @xlog2 = log2(@x);



Return the log base ten of the argument. A list form of the function is also provided.

sign()



    $s = sign($x);
    @valsigns = sign(@values);



Returns -1 if the argument is negative, 0 if the argument is zero, and 1 if the argument is positive.

In list form it applies the same operation to each member of the list.

copysign()



    $ms = copysign($m, $n);
    $s = copysign($x);



Take the sign of the second argument and apply it to the first. Zero is considered part of the positive signs.



    copysign(-5, 0);  # Returns 5.
    copysign(-5, 7);  # Returns 5.
    copysign(-5, -7); # Returns -5.
    copysign(5, -7);  # Returns -5.



If there is only one argument, return -1 if the argument is negative, otherwise return 1. For example, copysign(1, -4) and copysign(-4) both return -1.

flipsign()



    $ms = flipsign($m, $n);



Multiply the signs of the arguments and apply it to the first. As with copysign(), zero is considered part of the positive signs.

Effectively this means change the sign of the first argument if the second argument is negative.



    flipsign(-5, 0);  # Returns -5.
    flipsign(-5, 7);  # Returns -5.
    flipsign(-5, -7); # Returns 5.
    flipsign(5, -7);  # Returns -5.



If for some reason flipsign() is called with a single argument, that argument is returned unchanged.

floor()



    $b = floor($a/2);

    @ilist = floor(@numbers);



Returns the greatest integer less than or equal to its argument. A list form of the function also exists.



    floor(1.5, 1.87, 1);        # Returns (1, 1, 1)
    floor(-1.5, -1.87, -1);     # Returns (-2, -2, -1)



ceil()



    $b = ceil($a/2);

    @ilist = ceil(@numbers);



Returns the lowest integer greater than or equal to its argument. A list form of the function also exists.



    ceil(1.5, 1.87, 1);        # Returns (2, 2, 1)
    ceil(-1.5, -1.87, -1);     # Returns (-1, -1, -1)



moduli()

Return the moduli of a number after repeated divisions. The remainders are returned in a list from left to right.



    @rems = moduli(29, 3);        # Returns (2, 0, 0, 1)
    @digits = moduli(1899, 10);   # Returns (9, 9, 8, 1)



    compare tag

Create comparison functions for floating point (non-integer) numbers.

Since exact comparisons of floating point numbers tend to be iffy, the comparison functions use a tolerance chosen by you. You may then use those functions from then on confident that comparisons will be consistent.

If you do not provide a tolerance, a default tolerance of 1.49012e-8 (approximately the square root of an Intel Pentium’s machine epsilon <http://en.wikipedia.org/wiki/Machine_epsilon>) will be used.

generate_fltcmp()

Returns a comparison function that will compare values using a tolerance that you supply. The generated function will return -1 if the first argument compares as less than the second, 0 if the two arguments compare as equal, and 1 if the first argument compares as greater than the second.



    my $fltcmp = generate_fltcmp(1.5e-7);

    my(@xpos) = grep {&$fltcmp($_, 0) == 1} @xvals;



generate_relational()

Returns a list of comparison functions that will compare values using a tolerance that you supply. The generated functions will be the equivalent of the equal, not equal, greater than, greater than or equal, less than, and less than or equal operators.



    my($eq, $ne, $gt, $ge, $lt, $le) = generate_relational(1.5e-7);

    my(@approx_5) = grep {&$eq($_, 5)} @xvals;



Of course, if you were only interested in not equal, you could use:



    my(undef, $ne) = generate_relational(1.5e-7);

    my(@not_around5) = grep {&$ne($_, 5)} @xvals;



    polynomial tag

Perform some polynomial operations on plain lists of coefficients.



    #
    # The coefficient lists are presumed to go from low order to high:
    #
    @coefficients = (1, 2, 4, 8);    # 1 + 2x + 4x**2 + 8x**3



In all functions the coeffcient list is passed by reference to the function, and the functions that return coefficients all return references to a coefficient list.

<B>It is assumed that any leading zeros in the coefficient lists have already been removed before calling these functions, and that any leading zeros found in the returned lists will be handled by the caller.B> This caveat is particulary important to note in the case of pl_div().

Although these functions are convenient for simple polynomial operations, for more advanced polynonial operations Math::Polynomial is recommended.

pl_evaluate()



    $y = pl_evaluate(\@coefficients, $x);
    @yvalues = pl_evaluate(\@coefficients, \@xvalues);



Returns either a y-value for a corresponding x-value, or a list of y-values on the polynomial for a corresponding list of x-values, using Horner’s method.

pl_dxevaluate()



    ($y, $dy, $ddy) = pl_dxevaluate(\@coefficients, $x);



Returns p(x), p’(x), and p"(x) of the polynomial for an x-value, using Horner’s method. Note that unlike pl_evaluate() above, the function can only use one x-value.

pl_add()



    $polyn_ref = pl_add(\@m, \@n);



Add two lists of numbers as though they were polynomial coefficients.

pl_sub()



    $polyn_ref = pl_sub(\@m, \@n);



Subtract the second list of numbers from the first as though they were polynomial coefficients.

pl_div()



    ($q_ref, $r_ref) = pl_div(\@numerator, \@divisor);



Synthetic division for polynomials. Divides the first list of coefficients by the second list.

Returns references to the quotient and the remainder.

Remember to check for leading zeros (which are rightmost in the list) in the returned values. For example,



    my @n = (4, 12, 9, 3);
    my @d = (1, 3, 3, 1);

    my($q_ref, $r_ref) = pl_div(\@n, \@d);



After division you will have returned (3) as the quotient, and (1, 3, 0) as the remainder. In general, you will want to remove the leading zero in the remainder.

pl_mult()



    $m_ref = pl_mult(\@coefficients1, \@coefficients2);



Returns the reference to the product of the two multiplicands.

pl_derivative()



    $poly_ref = pl_derivative(\@coefficients);



Returns the derivative of a polynomial.

pl_antiderivative()



    $poly_ref = pl_antiderivative(\@coefficients);



Returns the antiderivative of a polynomial. The constant value is always set to zero and will need to be changed by the caller if a different constant is needed.



  my @coefficients = (1, 2, -3, 2);
  my $integral = pl_antiderivative(\@coefficients);

  #
  # Integral needs to be 0 at x = 1.
  #
  my @coeff1 = @{$integral};
  $coeff1[0] = - pl_evaluate($integral, 1);



AUTHOR

John M. Gamble, <jgamble at cpan.org>

SEE ALSO

Math::Polynomial for a complete set of polynomial operations, with the added convenience that objects bring.

Among its other functions, List::Util has the mathematically useful functions max(), min(), product(), sum(), and sum0().

List::MoreUtils has the function minmax().

Math::Prime::Util has gcd() and lcm() functions, as well as vecsum(), vecprod(), vecmin(), and vecmax(), which are like the List::Util functions but which can force integer use, and when appropriate use Math::BigInt.

Math::VecStat Likewise has min(), max(), sum() (which can take as arguments array references as well as arrays), plus maxabs(), minabs(), sumbyelement(), convolute(), and other functions.

BUGS

Please report any bugs or feature requests to bug-math-util at rt.cpan.org, or through the web interface at <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Math-Utils>. I will be notified, and then you’ll automatically be notified of progress on your bug as I make changes.

SUPPORT

This module is on Github at <https://github.com/jgamble/Math-Utils>.

You can also look for information at:
o RT: CPAN’s request tracker (report bugs here)

<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Math-Utils>

o AnnoCPAN: Annotated CPAN documentation

<http://annocpan.org/dist/Math-Utils>

o CPAN Ratings

<http://cpanratings.perl.org/d/Math-Utils>

o Search CPAN

<http://search.cpan.org/dist/Math-Utils/>

ACKNOWLEDGEMENTS

To J. A. R. Williams who got the ball rolling with Math::Fortran.

LICENSE AND COPYRIGHT

Copyright 2015 by John M. Gamble

This program is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

<http://www.perlfoundation.org/artistic_license_2_0>

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