# NAME

Math::Symbolic::Constant - Constants in symbolic calculations

# SYNOPSIS

```
use Math::Symbolic::Constant;
my $const = Math::Symbolic::Constant->new(25);
my $zero = Math::Symbolic::Constant->zero();
my $one = Math::Symbolic::Constant->one();
my $euler = Math::Symbolic::Constant->euler();
# e = 2.718281828...
```

# DESCRIPTION

This module implements numeric constants for Math::Symbolic trees.

## EXPORT

None by default.

# METHODS

## Constructor new

Takes hash reference of key-value pairs as argument. Special case: a value for the constant instead of the hash. Returns a Math::Symbolic::Constant.

## Constructor zero

Arguments are treated as key-value pairs of object attributes. Returns a Math::Symbolic::Constant with value of 0.

## Constructor one

Arguments are treated as key-value pairs of object attributes. Returns a Math::Symbolic::Constant with value of 1.

## Constructor euler

Arguments are treated as key-value pairs of object attributes. Returns a Math::Symbolic::Constant with value of e, the Euler number. The object has its 'special' attribute set to 'euler'.

## Constructor pi

Arguments are treated as key-value pairs of object attributes. Returns a Math::Symbolic::Constant with value of pi. The object has its 'special' attribute set to 'pi'.

## 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 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 special

Optional argument: sets the object's special attribute. Returns the object's special attribute.

## Method to_string

Returns a string representation of the constant.

## Method term_type

Returns the type of the term. (T_CONSTANT)

# 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/