NAME
DateTime::Util::Calc - DateTime Calculation Utilities
SYNOPSIS
use DateTime::Util::Calc qw(polynomial);
my @coeffs = qw(2 3 -2);
my $x = 5;
my $rv = polynomial($x, @coeffs);
DESCRIPTION
This module contains some common calculation utilities that are required
to perform datetime calculations, specifically from "Calendrical
Calculations" -- they are NOT meant to be general purpose.
Nothing is exported by default. You must either explicitly export them,
or use as fully qualified function names.
FUNCTIONS
max($a, $b)
min($a, $b)
max() returns the bigger of $a and $b. min() returns the smaller of $a
and $b.
polynomial($x, @coefs)
Calculates the value of a polynomial equation, based on Horner's Rule.
c + b * x + a * (x ** 2) x = 5
is expressed as:
polynomial(5, c, b, a);
moment($dt)
dt_from_moment($moment)
moment() converts a DateTime object to moment, which is RD days + the
time of day as fraction of the total seconds in a day.
dt_from_moment() converts a moment to DateTime object.
rata_die()
Returns a new DateTime object that is set to Rata Die, 0001-01-01
00:00:00 UTC
bigfloat($v)
bigint($v)
If the value $v is not a Math::BigFloat object, returns the value
converted to Math::BigFloat. Otherwise returns the value itself.
bigint() does the same for Math::BigInt.
bf_downgrade($v)
bi_downgrade($v)
If the value $v is a Math::BigFloat object, returns the "downgraded",
regular Perl scalar version of $v. This is sometimes required for
functions or objects that do not accept Math::BigFloat.
If $v is not Math::BigFloat object, just returns the value itself.
bi_downgrade() does the same for Math::BigInt.
truncate_to_midday($dt)
Truncates the DateTime object to 12:00 noon.
sin_deg($degrees)
cos_deg($degrees)
tan_deg($degrees)
asin_deg($degrees)
acos_deg($degrees)
Each of these functions calculates their respective values based on
degrees, not radians (as Perl's version of sin() and cos() would do).
Since Math::BigFloat does not have corresponding trigonemetric
functions, values passed to these funtions will be automatically
downgraded via bf_downgrade()
mod($v,$mod)
Calculates the modulus of $v over $mod. Perl's built-in modulus operator
(%) for some reason rounds numbers UP when a fractional number's modulus
is taken. Many of the calculations also needed the fractional part of
the calculation, so this function takes care of both.
Example:
mod(12.234, 5) = 2.234
amod($v,$mod)
This function is almost identical to mod(), but when the regular modulus
value is 0, returns $mod instead of 0.
Example:
amod(11, 5) = 1
amod(10, 5) = 5
amod(9, 5) = 4
amod(8, 5) = 3
binary_search($hi, $lo, $mu, $phi)
This is a special version of binary search, where the terminating
condition is determined by the result of coderefs $mu and $phi.
$mu is passed the value of $hi and $lo. If it returns true upon
execution, then the search terminates.
$phi is passed the next median value. If it returns true upon execution,
then the search terminates.
If the above two fails, then $hi and $lo are re-computed for the next
iteration.
search_next(%opts)
Performs a "linear" search until some condition is met. This is a
generalized version of the formula defined in [1] p.22. The basic idea
is :
x = base
while (! check(x) ) {
x = next(x);
}
return x
%opts can contain the following parameters:
base
The initial value to use to start the search process. The value can
be anything, but you must provide "check" and "next" parameters that
are capable of handling the type of thing you specified.
check (coderef)
Code to be executed to determine the end of the search. The function
receives the current value of "x", and should return a true value if
the condition to end the loop has been reached
next (coderef, optional)
Code to be executed to determine the next value of "x". The function
receives the current value of "x", and should return the value to be
used for the next iteration.
If unspecified, it will use a function that blindly adds 1 to
whatever x is. (so if you specified a number for "base", it should
work -- but if you passed an object like DateTime, it will probably
be an error)
So for example, to iterate through 1 through 9, you could do something
like this
my $x = search_next(
base => 1,
check => sub { $_[0] == 9 }
);
And $x will be set to 9. For a more interesting example, we could look
for a DateTime object $dt matching a certain condition "foo()":
my $dt = search_next(
base => $base_date,
check => \&foo,
next => sub { $_[0] + DateTime::Duration->new(days => 1) }
);
revolution($angle_in_degrees)
Reduces any angle to within the first revolution by sbtracting or adding
even multiples of 360.0.
rev180($angle_in_degrees)
Reduces input to within +180..+180 degrees
angle($h, $m, $s)
CAVEATS
For performance reasons, there is absolutely no parameter validation via
Params::Validate in this module!
AUTHOR
(c) Copyright 2004-2005 Daisuke Maki . All rights
reserved.