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DifferentialGeometry

  

InverseTransformation

  

find the inverse of a transformation

 

Calling Sequence

Parameters

Description

Examples

Calling Sequence

InverseTransformation(Phi, options)

Parameters

Phi

-

a transformation mapping one manifold M to another manifold N

options

-

branch = "all" or branch = [pt1, pt2], where pt2 is a list of coordinates (Maple expressions) defining a point in M and Phi(pt2) = pt1

Description

• 

The InverseTransformation command uses the Maple solve command to find a (local) inverse transformation Psi: N -> M, that is, Psi o Phi = identity on M and Phi o Psi = identity on N.

• 

Use the Maple environment variable _EnvExplicit = true to obtain explicit formulas for the inverse.

• 

In the case where there are multiple local inverses, the first one in the list returned by solve is returned by InverseTransformation.  

• 

With branch = "all", InverseTransformation returns a list of all the inverse transformations.

• 

With branch = [pt1, pt2], InverseTransformation returns the particular inverse transformation Psi satisfying Psi(pt1) = pt2.

• 

This command is part of the DifferentialGeometry package, and so can be used in the form InverseTransformation(...) only after executing the command with(DifferentialGeometry).  It can always be used in the long form DifferentialGeometry:-InverseTransformation.

Examples

withDifferentialGeometry:

 

Define a pair of 2-dimensional manifolds.

DGsetupx,y,M:DGsetupu,v,N:

 

Example 1.

Define a simple transformation Phi1: M -> N with a unique global inverse.

Φ1TransformationM,N,u=2x3y,v=x+2y

Φ1u=2x3y,v=x+2y

(1)

Ψ1InverseTransformationΦ1

Ψ1x=2u+3v,y=2v+u

(2)

Use ComposeTransformations to checks the result of InverseTransformation.

ComposeTransformationsΨ1,Φ1

x=x,y=y

(3)

ComposeTransformationsΦ1,Ψ1

u=u,v=v

(4)

 

Example 2.

Define a transformation  Phi2: M -> N  with multiple local inverses.

Φ2TransformationM,N,u=x2,v=y2

Φ2u=x2,v=y2

(5)

Ψ2InverseTransformationΦ2

Ψ2x=RootOf_Z2u,y=RootOf_Z2v

(6)

To get explicit solutions:

_EnvExplicittrue

_EnvExplicittrue

(7)

Ψ2InverseTransformationΦ2

Ψ2x=u,y=v

(8)

To get all possible inverses:

AllInversesInverseTransformationΦ2,branch=all

AllInversesx=u,y=v,x=u,y=v,x=u,y=v,x=u,y=v

(9)

Since Phi2([- 1, - 1]) = [1, 1], we can ask for that particular inverse which maps [1, 1] to [- 1, - 1].  We can use either [1, 1] or [u = 1, v = 1] as arguments in the command InverseTransformation to indicate the coordinates of the point.

InverseTransformationΦ2,branch=1,1,1,1

x=u,y=v

(10)

InverseTransformationΦ2,branch=u=1,v=1,x=1,y=1

x=u,y=v

(11)
M > 

See Also

DifferentialGeometry

ComposeTransformations

Transformation

 


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