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HELP FOR: grtransform
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CALLING SEQUENCE: grtransform ( oldmetric, newmetric, xform, [sig] )

      PARAMETERS: oldmetric - the name of the metric to be transformed
                  newmetric - the name by which the transformed metric is
                               to be referenced
                  xform     - a list specifying the transformation
                  sig       - (optional) the signature of the new metric,
                               if different from the old.
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SYNOPSIS:

- Performs a coordinate transformation of the metric tensor.

- The transformation is specified by a list of functions giving the
  old coordinates in terms of the new coordinates or vice versa. For
  instance if we are performing the transformation

                [t,x,y,z] --> [tau,u,v,w]

  then we could specify xform as a set of functions of old in terms
  of new,

      xform := [ t(tau,u,v,w)=..., x(tau,u,v,w)=..., y(tau,u,v,w)=..., 
               z(tau,u,v,w) = ... ]:

  or new in terms of old,

      xform := [ tau(t,x,y,z)=..., u(t,x,y,z)=..., v(t,x,y,z)=..., 
               w(t,x,y,z)=... ]:

- Note that for an n-dimensional spacetime, n functions must be specified.

- None of the new set of coordinates can be the same as any of the old
  coordinates. For instance, if both spacetimes are spherically symmetric,
  new coordinate names for the angles must be given.

- It is not necessary that each of the transformation functions be specified 
  as a function of all n variables, but each of the variables must be
  represented in at least one of the functions of the set. For instance,
  in the second example above, at least one of the components of xform
  must be a function of t, at least one must be a function of x, etc.

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EXAMPLES:

> qload ( schw ):

> xform := [ u(r,t) = sqrt(r/(2*m)-1)*exp(r/(4*m))*cosh(t/(4*m)),
>            v(r,t) = sqrt(r/(2*m)-1)*exp(r/(4*m))*sinh(t/(4*m)),
>            Theta(theta) = theta,
>            Phi(phi) = phi ];

> grtransform ( schw, kruskal, xform ):

   The new default metric is: kruskal

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SEE ALSO: makeg, grsaveg, grmap, grconstraint, nptetrad, nprotate.
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