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Example 1. Use the first calling sequence to set up up a coordinate system on a manifold.
In this first example, we create a 2dimensional manifold M with coordinates [x, y].
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The coordinates are now protected names which cannot be assigned values.
The standard coordinate vectors D_x, D_y and dual 1 forms dx, dy have been defined and protected. We display the internal representation of these vectors just to show that they have been assigned values. (Knowledge of this internal representation of various objects used in the DifferentialGeometry package is not required of the user).
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_DG([["vector", M, []], [[[1], 1]]])
 
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_DG([["form", M, 1], [[[1], 1]]])
 
Without the option 'verbose', the information concerning the definition and protection of variable is suppressed. This behavior of the DGsetup command can be controlled globally with the Preferences command.
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Example 2. Use the second calling sequence to set up coordinates on a vector or fiber bundle.
In many situations in differential geometry, one deals with vector bundles or fiber bundles pi: E > M. For these applications, use the second calling sequence to DGsetup. The
first argument varlist1 should be coordinates for the basis manifold M and the second argument should be the list of coordinates for the fiber of the bundle E. Here is the command
for creating a rank2 bundle over a 3dimensional space. The base coordinates are [x, y, z] and the fiber coordinates are [u, v].
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This particular use of DGsetup could be used, for example, to study a 3dimensional manifold imbedded in a 5dimensional Riemannian manifold, where the vectors D_u and D_v define a local basis for the normal bundle.
Example 3. Use the third calling sequence to set up coordinates on a jet bundle. The JetCalculus subpackage of the DifferentialGeometry package contains an extensive set of commands for symbolic computations on jet spaces. These spaces provide the natural mathematical setting for the geometric approach to the calculus of variations and to differential equations. The third calling sequence for the DGsetup command will create a jet space over a bundle pi: E > M with prescribed lists of independent variables (coordinates on M) and dependent variables (fiber coordinates on E). In addition to the coordinate vectors and coordinate differential forms on jet space, DGsetup also defines and protects the contact forms on jet space. See the JetCalculus overview page for additional information regarding these differential forms. The user may specify which of two notational conventions are to be used to denote the jet coordinates. See the Preferences command for details.
First we initialize the 3rd order jet space for 1 independent and 2 dependent variables.
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Here is the initialization of the 3rd order jet space for 2 independent and 1 dependent variable.
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Example 4. Use the fourth calling sequence to set up an anholonomic frame on a manifold.
It is extremely important, for many calculations in DifferentialGeometry, to work with frames and coframes other than the coordinate frame (e.g. D_x, D_y, ...) and the coordinate coframe (e.g. dx, dy ...). For example, curvature tensor calculations are often greatly simplified by working in an orthonormal frame. To set up a frame for subsequent computations with the DifferentialGeometry package, first use the FrameData command to calculate the structure equations for the frame or coframe. Then pass the output of the FrameData command to DGsetup.
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The three vectors in the list F are the vectors that will be used as a frame.
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The command FrameData calculates the structure equations for this frame. These structure equations are displayed with the convention that the first element of the frame is E1, the second element is E2, and so on. The name of the manifold with coordinates [x, y, z] and anholonomic frame F is M1.
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Pass the output of FrameData to the command DGsetup. Now in place of the coordinate vectors D_x, D_y, D_z and coordinate form dx, dy, dz, we shall use the vectors F[1], F[2], F[3] and the dual 1 forms. The default labels for the frame elements are E1, E2, E3 and the default labels for the coframe elements are Theta1, Theta2, Theta3.
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As sample calculations on the manifold M1 we have:
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We can specify the labels for the frame and the coframe as optional arguments to DGsetup. The second argument is a list of names for the frame elements and the third argument is a list of names for the coframe elements. If a list with just one name is given, then that name is used as the kernel name for the list of frame or coframe elements. For example:
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Example 5. Use the fourth calling sequence to set up an anholonomic coframe on a manifold.
The same commands used in the previous example can be used to create an anholonomic coframe on a manifold.
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The three 1foms in the list Omega are the 1forms that will be used as a coframe.
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The command FrameData calculates the structure equations for this coframe. These structure equations are displayed with the convention that the first element of the frame is 1, the second element is 2, and so on. The name of the manifold with coordinates [x, y, z] and anholonomic frame Omega is M1.
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Pass the output of FrameData to the command DGsetup. Now in place of the coordinate vectors D_x, D_y, D_z and coordinate form dx, dy, dz, we shall use the 1forms Omega[1], Omega[2], Omega[3] and the dual vector fields. The default labels for the frame elements are E1, E2, E3 and the default labels for the coframe elements are Theta1, Theta2, Theta3.
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Example 6. Use the fifth calling sequence to initialize a Lie algebra, defined by a set of matrices
The DGsetup command can also be used to initialize a Lie algebra the same way that DGsetup is used to initialize an anholonomic frame on a manifold. Typically, one first obtains the structure equations for the Lie algebra using the LieAlgebraData command and then passes these structure equations to DGsetup. Structure equations for a large number of Lie algebras can also be retrieved from the database of Lie algebras found in the Library package.
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Calculate the structure equations for the matrix Lie algebra defined by the matrices M. Here e1 refers to the first matrix in M, e2 the second matrix, ....
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The default names for the basis elements for the Lie algebra are e1, e2, e3.... The default names for the basis elements for the dual elements of the Lie algebra are theta1, theta2, ....
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Again it is a simple matter to override this default labeling.
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Example 7. Use the fifth calling sequence to initialize a Lie algebra, defined by a set of vector fields
The same sequence of commands as illustrated in the previous example can be used to initialize a Lie algebra from a set of vector fields.
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Here are the vector fields we shall use.
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Example 8. Use the fifth calling sequence to initialize a simple Lie algebra, defined by structure equations
The LieAlgebraData command, in conjunction with DGsetup, can be used to initialize a Lie algebra from a set of structure equations. First specify the basis elements. These must be unassigned names.
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Define a list of structure equations for a Lie algebra.
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Example 9. Use the fifth calling sequence to initialize a simple Lie algebra, constructed from the command SimpleLieAlgebraData
The LieAlgebra package contains tables of structures equations for the classical simple and semisimple matrix algebras. These can be accessed with the command SimpleLieAlgebraData. In this example we initialize , the Lie algebra of tracefree matrices.
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Example 10. Use the sixth calling sequence to initialize a Lie algebra with coefficients in a representation
Exterior forms on Lie algebras can be generalized to allow for coefficients in a representation. In this example we use the 3dimensional Lie algebra defined in Example 7 and its adjoint representation. First, define a 3dimensional space to serve as the representation space.
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Now use the Adjoint and Representation commands to create the adjoint representation for .
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Invoke the sixth calling sequence for DGsetup.
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At this point one can calculate, for example, the exterior derivative of a 1form on alg7 with coefficients in V.
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Example 11. Use the seventh calling sequence to initialize a list of abstract differential forms
In this example we use DGsetup to define a computational environment defined by a single scalar , a 1form and a 2form . The exterior derivative of is specified as .
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We use DGsetup to add forms or structure equations.
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Example 12. Use the seventh calling sequence to initialize a coframe and a list of abstract differential forms
This is essentially the same as Example 11 except that the first list, used to specify the list of abstract forms, now contains a sublist defining a coframe. In this example, we would like to label the coframe as but these names were assigned to the 1forms for the Lie algebra . Therefore, we should first remove this frame.
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In this setting interior products and Lie derivatives can be computed.
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M12 >


For more information on abstract differential forms in DifferentialGeometry, see WorkingWithAbstractForms.