# NAME

Math::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 M�ller, symbolic-module at steffen-mueller dot net
Stray Toaster, mwk at users dot sourceforge dot net
Oliver Ebenh�h
```

# 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/