Math::Symbolic::Variable - Variable in symbolic calculations
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,
}
);
This class implements variables for Math::Symbolic trees. The objects are
overloaded in stringification context to return their names.
None by default.
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.
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.
Optional argument: sets the object's name. Returns the object's name.
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.
explicit_signature() returns a lexicographically sorted list of variable
names in the tree.
See also:
signature().
set_signature expects any number of variable identifiers as arguments. It sets a
variable's signature to this list of identifiers.
Returns a string representation of the variable.
Returns the type of the term. (T_VARIABLE)
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
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