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HELP FOR: kdelta
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SYNOPSIS:

- The kdelta{^a b} object is used to represent the Kronecker delta matrix:

                  kdelta{^a b} :=  1 if a = b,
                                   0 otherwise.

- It can be used in grdef() to define new objects, for instance:

        > grdef ( `T{^a b} := phi(t)*kdelta{^a b}` ):


- It can also be used in grdef() to select a single component of a tensor.
  The component is selected by prefixing its name with a dollar sign `$',
  as in:

        > grdef ( `v{^a} := kdelta{ ^a $t }` ):

  If the components are {r,theta,phi,t} then this command is equivalent
  to
        > grdef ( `v{^a} := [ 0, 0, 0, psi(t) ]` ):

  however in the previous case, one would still need to run grcalc( v(up) )
  to assign the components of v.

- kdelta is defined automatically and can not be calculated or displayed or
  altered as other tensors.

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EXAMPLE:

> qload ( schw ):

> grdef ( `T{^a ^b} := rho(t)*kdelta{^a $t}*kdelta{^b $t}` ):

> grcalc ( T(up,up) ):
Calculated T2(up,up) for schw. (0.080000 sec.) 

> grdisplay ( _ ):

 
                            For the schw spacetime:
 
                                    T(up,up)
 
                                  [ 0  0  0     0   ]
                                  [                 ]
                            a b   [ 0  0  0     0   ]
                           T    = [                 ]
                                  [ 0  0  0     0   ]
                                  [                 ]
                                  [ 0  0  0  rho(t) ]

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SEE ALSO: grdef, grt_objects.
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