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 MXller, symbolic-module at steffen-mueller dot net
         Stray Toaster, mwk at users dot sourceforge dot net
         Oliver EbenhXh

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