TODO write precision values into module available for the precision() sub my %precision; sub store_precision { my ($name, $precision, $type) = @_;
if ($type eq 'defined') {
$type = 'relative';
$precision = 0;
}
$precision{$name}->{value} = $precision;
$precision{$name}->{type} = $type;
}sub write_precision { my ($fh) = @_;
say $fh 'my %_precision = (';
for my $name (sort keys %precision) {
my ($value, $type) = @{$precision{$name}}{qw(value type)};
say $fh "\t$name \t=> {value => $value, \ttype => '$type'},";
}
say $fh ');';
}SYNOPSIS
use strict;
use Astro::Constants qw( :all );
# to calculate the gravitational force of the Sun on the Earth
# in Newtons, use GMm/r^2
my $force_sun_earth = GRAVITATIONAL * MASS_SOLAR * MASS_EARTH / ASTRONOMICAL_UNIT**2;DESCRIPTION
This module provides physical and mathematical constants for use in Astronomy and Astrophysics.
The values are stored in Physical_Constants.xml in the data directory and are mostly based on the 2018 CODATA values from NIST.
NOTE: Other popular languages are still using 2014 CODATA values for their constants and may produce different results in comparison. On the roadmap is a set of modules to allow you to specify the year or data set for the values of constants, defaulting to the most recent.
The :all tag imports all the constants in their long name forms (i.e. GRAVITATIONAL). Useful subsets can be imported with these tags: :fundamental :conversion :mathematics :cosmology :planetary :electromagnetic or :nuclear. Alternate names such as LIGHT_SPEED instead of SPEED_LIGHT or HBAR instead of H_BAR are imported with :alternates. I'd like to move away from their use, but they have been in the module for years.
Long name constants are constructed with the constant pragma and are not interpolated in double quotish situations because they are really inlined functions. Short name constants were constructed with the age-old idiom of fiddling with the symbol table using typeglobs, e.g. *PI = \3.14159, and can be slower than the long name constants.
Why use this module
You are tired of typing in all those numbers and having to make sure that they are all correct. How many significant figures is enough or too much? Where's the definitive source, Wikipedia? And which mass does "$m1" refer to, solar or lunar?
The constant values in this module are protected against accidental re-assignment in your code. The test suite protects them against accidental finger trouble in my code. Other people are using this module, so more eyeballs are looking for errors and we all benefit. The constant names are a little longer than you might like, but you gain in the long run from readable, sharable code that is clear in meaning. Your programming errors are a little easier to find when you can see that the units don't match. Isn't it reassuring that you can verify how a number is produced and which meeting of which standards body is responsible for its value?
Trusting someone else's code does carry some risk, which you should consider, but have you also considered the risk of doing it yourself with no one else to check your work? And, are you going to check for the latest values from NIST every 4 years?
And plus, it's FASTER
Benchmarking has shown that the imported constants can be more than 3 times faster than using variables or other constant modules because of the way the compiler optimizes your code. So, if you've got a lot of calculating to do, this is the module to do it with.
EXPORT
Nothing is exported by default, so the module doesn't clobber any of your variables. Select from the following tags:
FUNCTIONS
pretty
This is a helper function that rounds a value or list of values to 5 significant figures.
precision
Give this method the string of the constant and it returns the precision or uncertainty listed.
$rel_precision = precision('GRAVITATIONAL');
$abs_precision = precision('MASS_EARTH');At the moment you need to know whether the uncertainty is relative or absolute. Looking to fix this in future versions.
Deprecated functions
I've gotten rid of list_constants and describe_constants because they are now in the documentation. Use perldoc Astro::Constants for that information.
SEE ALSO
Reference Documents:
REPOSITORY
* github
ISSUES
Feel free to file bugs or suggestions in the Issues section of the Github repository.
Using strict is a must with this code. Any constants you forgot to import will evaluate to 0 and silently introduce errors in your code. Caveat Programmer.
If you are using this module, drop me a line using any available means at your disposal, including *gasp* email (address in the Author section), to let me know how you're using it. What new features would you like to see?
Current best method to contact me is via a Github Issue.
Extending the data set
If you want to add in your own constants or override the factory defaults, run make, edit the PhysicalConstants.xml file and then run dzil build again. If you have a pre-existing PhysicalConstants.xml file, drop it in place before running dzil build.
Availability
the original astroconst sites have disappeared
ROADMAP
I have moved to a noun_adjective format for long names. LIGHT_SPEED and SOLAR_MASS become SPEED_LIGHT and MASS_SOLAR. This principle should make the code easier to read with the most important information coming at the beginning of the name. See also Astro::Constants::Roadmap
ASTROCONST
(Gleaned from the Astroconst home page - astroconst.org )
Astroconst is a set of header files in various languages (currently C, Fortran, Perl, Java, IDL and Gnuplot) that provide a variety of useful astrophysical constants without constantly needing to look them up.
The generation of the header files from one data file is automated, so you can add new constants to the data file and generate new header files in all the appropriate languages without needing to fiddle with each header file individually.
This package was created and is maintained by Jeremy Bailin. It's license states that it is completely free, both as in speech and as in beer.
DISCLAIMER
No warranty expressed or implied. This is free software. If you want someone to assume the risk of an incorrect value, you better be paying them.
(What would you want me to test in order for you to depend on this module?)
from Jeremy Bailin's astroconst header files
The Astroconst values have been gleaned from a variety of sources, and have quite different precisions depending both on the known precision of the value in question, and in some cases on the precision of the source I found it from. These values are not guaranteed to be correct. Astroconst is not certified for any use whatsoever. If your rocket crashes because the precision of the lunar orbital eccentricity isn't high enough, that's too bad.
ACKNOWLEDGMENTS
Jeremy Balin, for writing the astroconst package and helping test and develop this module.
Doug Burke, for giving me the idea to write this module in the first place, tidying up Makefile.PL, testing and improving the documentation.
<%= $c->{value} %><%= q{ } . $unit if $unit %><%= $c->{description} %> <% if ($c->{alternates}) { %> % if ($c->{alternates}->@* > 1) { This constant is also available using these alternate names (imported using the :alternate tag): <%= join ', ', $c->{alternates}->@* %> % } else { This constant is also available using the alternate name <%= $c-{alternates}[0] %>> (imported using the :alternate tag for backwards compatibility) % } <% } %> EOT }, );
unless (exists $template{$style}) {
carp "No templates available for $style. Using default 'perl'\n";
$style = 'perl';
}
return $template{$style}->%*;
}sub show_usage { return "Usage: $0 [hnostv] xml_file(s)\n"; }
sub store_precision { my ($name, $precision, $type) = @_;
if ($type eq 'defined') {
$type = 'relative';
$precision = 0;
}
$precision{$name}->{value} = $precision;
$precision{$name}->{type} = $type;
}sub extract_constant { my $element = shift;
my $name = $element->getChildrenByTagName('name')->shift()->textContent();
my $description = $element->getChildrenByTagName('description')->shift()->textContent();
chomp $description;
my $constant = {
name => $name,
value => $element->getChildrenByTagName('value')->shift()->textContent(),
description => $description,
};
# recognise that there can be more than one alternateName
my $alternate = undef;
my @alternates = ();
if ( $element->getChildrenByTagName('alternateName') ) {
for my $node ( $element->getChildrenByTagName('alternateName') ) {
$alternate = $node->textContent();
next unless $alternate =~ /\S/;
push @{$tagname->{alternates}}, $alternate;
if ($node->hasAttribute('type') && $node->getAttribute('type') eq 'deprecated') {
push @{$tagname->{deprecated}}, $alternate;
}
else {
push @{$tagname->{all}}, $alternate;
}
push @alternates, $alternate;
}
}
$constant->{alternates} = \@alternates if @alternates;
$constant->{deprecated} = 1 if $element->getChildrenByTagName('deprecated');
my @categories;
for my $cat_node ( $element->getElementsByTagName('category') ) {
my $category = $cat_node->textContent();
next unless $category;
push @categories, $category;
}
$constant->{categories} = \@categories if @categories;
my $precision = $element->getChildrenByTagName('uncertainty')->shift();
store_precision($name,
$precision->textContent(),
$precision->getAttribute('type'));
return $constant;
}1 POD Error
The following errors were encountered while parsing the POD:
- Around line 407:
Unknown directive: =constant