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HELP FOR: diffAlias
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CALLING SEQUENCE: diffAlias ( varlist, functionlist )

      PARAMETERS: varlist      - a set of variables (coordinates)
                  functionlist - a set of functions in the variables specified
                                 by varlist

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SYNOPSIS:

- Automatically creates aliases for derivatives in functions as per

                        d
                        -- u(r)  --->  u
                        dr              r

  in order to simplify the appearance of output.

- In contrast to autoAlias(), derivative aliases are only created for
  functions explicitly named in the second argument to diffAlias.

- The function makes use of the fact that arguments in square brackets
  are represented as subscripts in windows versions of MapleV. Thus, it
  will not help readability in terminal based MapleV.

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EXAMPLES:

# output for the following commands have been suppressed ...
> readlib ( grii ):
> h(r,t) := diff ( f(r,t), r )/r;

                                         d
                                       ---- f(r, t)
                                        dr
                            h(r, t) := ------------
                                             r

> diffAlias ( [r, t], [ f, g ] );
> k(r,t) := diff(h(r,t),t)*diff(g(r,t),r);
 
                                       f[t, r] g[r]
                            k(r, t) := ------------
                                             r

> #(Note that the square bracketed indices appear as subscripts in
> #   Windows-type displays.)

> qload ( bondi );

                           Default spacetime = bondi
 
                            For the bondi spacetime:
 
                                  Coordinates
 
                             a
                           x   = [ r, v, theta, phi ]
 
                                  Line element
 
    2                                  2 /      m(r, v)\     2     2         2
  ds  = 2 c(r, v)  d r  d  v  - c(r, v)  |1 - 2 -------|  d v   + r   d theta
                                         \         r   /
 
         2           2       2
      + r  sin(theta)   d phi
 

> diffAlias ( [r,v], [c,m] );
> grcalc ( R(dn,dn) );
> grdisplay ( _ );

                            For the bondi spacetime:
 
                                Covariant Ricci
 
                                             c[r]
                            R [r] [r] = 2 ---------
                                          c(r, v) r
 
                              - 2 c(r, v) m[r] + c[r] r - 2 c[r] m(r, v)
        R [theta] [theta] = - ------------------------------------------
                                                c(r, v)
 
  etc...

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SEE ALSO: autoAlias, grDalias.
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