Paul Miller

NAME

Math::Units::PhysicalValue - An OO interface for automatically calculating values with units.

SYNOPSIS

    use Math::Units::PhysicalValue;

    my $exit  = new Math::Units::PhysicalValue "10,000 ft";
    my $open  = "3500 ft";
    my $delay = "43 s";

    my $dist  = $exit - $open;
    my $rate  = $dist / $delay;

    my $weight = "180 lbs";
    my $momentum = ($weight * ( ($exit - $open) / $delay )) + "0 kg*m/s";

    print "$momentum\n";                     # prints 3,761.82 kg*m/s
    print ($rate + "0 miles/hour"), "\n"     # prints 103.07 miles/hour

DESCRIPTION

In more detail than the synopsis, Math::Units::PhysicalValue (aka PV) keeps track of the units on values that might work in the real world. It splits and stores the value and units separately as an array.

Using operator overloading, you can use them how you'd normally use any numeric value. There are probably more gotchas than I can enumerate, but you should be able to stay out of trouble if you keep string values on the right hand side of operators.

    my $example1 = new Math::Units::PhysicalValue "10,000 ft";  
    my $example2 = "3500 ft";
    my $example3 = "1000 ft";

    print ($example1 + $example2 + $example3), "\n"; # prints: 13,500 ft
    print ($example3 + $example2 + $example1), "\n"; # generates an error...

Perl is smart enough to do $example1 and $example2 in any order, but $example3 + $example2 is evaluated as the number 4500 (with no units) before it gets added to $example1 -- where the units won't match!

WATCH OUT FOR PLURALS

Math::Units can handle them (mostly), but Math::Algebra::Symbols cannot.

    my $v1 = new Math::Units::PhysicalValue "1 hour";
    my $v2 = new Math::Units::PhysicalValue "2 hours";
    my $v3 = $v1 + $v2;
    my $v4 = $v1 / $v2;

    print "$v3\n"; # prints 3 hours
    print "$v4\n"; # prints 0.5 hour/hours  .. and that's probably not what you want.

Export PV

There is a shortcut. You can use Math::Units::PhysicalValue "PV" to import the magical shortcut function. my $v = PV "10,000 ft" is the same as $example1 above. Handy.

    my $handy = (PV "8miles") + (PV "72ft");
    my $time  = PV "90s";
    my $fast  = $handy / $time;  # neato

You can also choose to import "pv" for this.

$StrictTypes

Presently, by default, you can create $wierd_units = PV "5 Saxons"; without any real trouble. When you try to convert it to something real, Math::Units will have an opportunity to complain. If your Saxon units cancel out before Math::Units sees it, though, it's perfectly fine to make it up as you go.

WATCH OUT FOR PLURALS (again) though.

$PrintPrecision

There is a Number::Format object in the head of PV. $PrintPrecision is the precision passed to format_number when PV is evaluated in a string context.

$Math::Units::PhysicalValue::PrintPrecision defaults to 2

You can set $Math::Units::PhysicalValue::PrintPrecision = -1 to disable it and lastly, you can set all sorts of format settings like so:

    $Math::Units::PhysicalValue::fmt = 
        new Number::Format(-thousands_sep   => '.',
                                -decimal_point   => ',',
                                -int_curr_symbol => 'DEM');

Though, at this time, there's no way to change which format function it uses.

deunit()

If you want to get the numerical value back out, you can use deunit();

    my $v = deunit PV("8 miles"); # makes $v = 8;

0 + PV or 0 - PV

I introduced a special hack on 12/7/5 to allow you to add ANY PV unit to 0 iff 0 had no units previously. That is:

    my $v = 0 + PV("3 ft"); # sets $v = PV("3 ft");

This functions by converting the scalar 0 to 0 ft before adding. If you wish to make sure to raise an error on addition to 0, choose to PV the 0 first.

   my $v = PV(0) + PV("3 ft"); # will still raise an error

AUTHOR

Paul Miller <jettero@cpan.org>

I am using this software in my own projects... If you find bugs, please please please let me know. If you use this at all, let me know. In fact, feel free to email me for almost any reason. So far, this policy has never been irritating.

COPYRIGHT

Copyright (c) 2009 Paul Miller -- LGPL2

TODO

Here's a list of things I'd still like to do.

If you'd like to add a couple, please float me an email.

1) Significant digit support (until it's done, there is $value-sci( $digits )>
2) Error interval support
3) (PV("7 m/s") ** 9) ** (1/9) should produce '7 m/s', not an error
*) Better handling of metric units (e.g, 3g == 0.003kg == 3000mg)

Concerning metric units, I expected them to work much worse than they do. In fact, they appear to function correctly. If you can produce and examples of failures, please let me know. For now I'm going to assume they work.

SPECIAL THANKS

Math::Units and Math::Algebra::Symbols do all the real work here.

So really, say thanks to these guys:

Ken Fox <fox ta vulpes.com>

Philip R Brenan at <philiprbrenan ta yahoo.com>

And here's a nod to Number::Format. I use the module constantly.

William R. Ward, <wrw ta bayview.com>

SEE ALSO

perl(1), Math::Units, Math::Algebra::Symbols, Number::Format




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