Math::Symbolic::VariabUser)Contributed Perl DocumenMath::Symbolic::Variable(3)NAMEMath::Symbolic::Variable - Variable in symbolic calculations
SYNOPSIS
use Math::Symbolic::Variable;
my $var1 = Math::Symbolic::Variable->new('name');
$var1->value(5);
my $var2 = Math::Symbolic::Variable->new('x', 2);
my $var3 =
Math::Symbolic::Variable->new(
{
name => 'variable',
value => 1,
}
);
DESCRIPTION
This class implements variables for Math::Symbolic trees. The objects
are overloaded in stringification context to return their names.
EXPORT
None by default.
METHODS
Constructor new
First argument is expected to be a hash reference of key-value pairs
which will be used as object attributes.
In particular, a variable is required to have a 'name'. Optional
arguments include a 'value', and a 'signature'. The value expected for
the signature key is a reference to an array of identifiers.
Special case: First argument is not a hash reference. In this case,
first argument is treated as variable name, second as value. This
special case disallows cloning of objects (when used as object method).
Returns a Math::Symbolic::Variable.
Method value
value() evaluates the Math::Symbolic tree to its numeric
representation.
value() without arguments requires that every variable in the tree
contains a defined value attribute. Please note that this refers to
every variable object, not just every named variable.
value() with one argument sets the object's value if you're dealing
with Variables or Constants. In case of operators, a call with one
argument will assume that the argument is a hash reference. (see next
paragraph)
value() with named arguments (key/value pairs) associates variables in
the tree with the value-arguments if the corresponging key matches the
variable name. (Can one say this any more complicated?) Since version
0.132, an equivalent and valid syntax is to pass a single hash
reference instead of a list.
Example: $tree->value(x => 1, y => 2, z => 3, t => 0) assigns the value
1 to any occurrances of variables of the name "x", aso.
If a variable in the tree has no value set (and no argument of value
sets it temporarily), the call to value() returns undef.
Method name
Optional argument: sets the object's name. Returns the object's name.
Method signature
signature() returns a tree's signature.
In the context of Math::Symbolic, signatures are the list of variables
any given tree depends on. That means the tree "v*t+x" depends on the
variables v, t, and x. Thus, applying signature() on the tree that
would be parsed from above example yields the sorted list ('t', 'v',
'x').
Constants do not depend on any variables and therefore return the empty
list. Obviously, operators' dependencies vary.
Math::Symbolic::Variable objects, however, may have a slightly more
involved signature. By convention, Math::Symbolic variables depend on
themselves. That means their signature contains their own name. But
they can also depend on various other variables because variables
themselves can be viewed as placeholders for more compicated terms. For
example in mechanics, the acceleration of a particle depends on its
mass and the sum of all forces acting on it. So the variable
'acceleration' would have the signature ('acceleration', 'force1',
'force2',..., 'mass', 'time').
If you're just looking for a list of the names of all variables in the
tree, you should use the explicit_signature() method instead.
Method explicit_signature
explicit_signature() returns a lexicographically sorted list of
variable names in the tree.
See also: signature().
Method set_signature
set_signature expects any number of variable identifiers as arguments.
It sets a variable's signature to this list of identifiers.
Method to_string
Returns a string representation of the variable.
Method term_type
Returns the type of the term. (T_VARIABLE)
AUTHOR
Please send feedback, bug reports, and support requests to the
Math::Symbolic support mailing list: math-symbolic-support at lists dot
sourceforge dot net. Please consider letting us know how you use
Math::Symbolic. Thank you.
If you're interested in helping with the development or extending the
module's functionality, please contact the developers' mailing list:
math-symbolic-develop at lists dot sourceforge dot net.
List of contributors:
Steffen MA~Xller, symbolic-module at steffen-mueller dot net
Stray Toaster, mwk at users dot sourceforge dot net
Oliver EbenhA~Xh
SEE ALSO
New versions of this module can be found on http://steffen-mueller.net
or CPAN. The module development takes place on Sourceforge at
http://sourceforge.net/projects/math-symbolic/
Math::Symbolic
perl v5.14.1 2011-07-26 Math::Symbolic::Variable(3)
