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PDEtools[CanonicalCoordinates] - compute canonical coordinates for a given symmetry
Calling Sequence
CanonicalCoordinates(S, DepVars, NewVars, CanVar, options=value)
Parameters
S
-
a list with the infinitesimals of a symmetry generator or the corresponding infinitesimal generator operator
DepVars
a function or a list of them indicating the (old) dependent variables of the problem
NewVars
optional - a function or a list of them representing the new dependent variables (canonical coordinates)
CanVar
optional - the name of the dependent variable with respect to which canonical coordinates are to be computed
jetnotation = ...
(optional) can be true (same as jetvariables), false (default), jetvariables, jetvariableswithbrackets, jetnumbers or jetODE; to respectively return or not using the different jet notations available
simplifier = ...
optional - indicates the simplifier to be used instead of the default
Description
Given a list with the infinitesimals of a symmetry generator, or the corresponding infinitesimal generator differential operator, the CanonicalCoordinates command computes a transformation from the dependent and independent variables of the problem to the canonical coordinates of the symmetry. This is the change of variables transforming the given list of infinitesimals into one consisting of zeros but for one element equal to 1. The corresponding transformed infinitesimal generator is thus of the form
where is a canonical dependent variable. For a problem with dependent variables.
There exist thus different sets of canonical coordinates leading to infinitesimals generators ofthe form above with different . To choose among them use Canvars to tell the name of the dependent variable of the problem with respect to which the canonical variables are computed. Canvars is not required when there is only one dependent variable.
When there is only one dependent variable, DepVars and NewVars can represented by a function; otherwise they must be a list of functions representing dependent variables. If NewVars are not given, CanonicalCoordinates will generate a list of globals to represent the canonical coordinates.
Optionally, a simplifier can be specified to be used instead of the default which is the composition of simplify and combine followed by a simplification in size
To avoid having to remember the optional keywords, if you type the keyword misspelled, or just a portion of it, a matching against the correct keywords is performed, and when there is only one match, the input is automatically corrected.
Examples
Consider a PDE problem with two independent variables and one dependent variable, , and consider the list of infinitesimals of a symmetry group
In the input above you can also enter the symmetry without infinitesimals' labels, as in . The corresponding infinitesimal generator is
In canonical coordinates -say - the infinitesimals of this symmetry are . The transformation from the original variables to the canonical coordinates is obtained via
In the input above, instead of you can also pass the symmetry without infinitesimals' labels, as in . You can also pass the infinitesimal generator differential operator as first argument instead of the list of infinitesimals
Solving now for you can change variables in the infinitesimals or its corresponding differential operator using ChangeSymmetry, achieving the expected form
If is not indicated, variables prefixed by the underscore _ to represent the canonical variables are introduced
To obtain the output in any particular jet notation, useful to perform computations with objects of type, name, e.g., differentiation with respect to a function but represented by a name, use the jetnotation option; compare for instance the output (4.5) with the following output
See Also
ChangeSymmetry, DEtools[canoni], InfinitesimalGenerator, PDEtools
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