| 
	    pltr0
	  ( | x, | 
| y, | |
| tx, | |
| ty, | |
| pltr_data ); | 
Identity transformation for matrix index to world coordinate mapping.  This routine
    can be used for the PLTRANSFORM_callback argument of plcont,
    plshade, plshades, plimagefr, or plvect.
x
	  (PLFLTX index of matrix.
y
	  (PLFLTY index of matrix.
tx
	  (PLFLT_NC_SCALARTransformed x value in world coordinates corresponding to x index of matrix.
ty
	  (PLFLT_NC_SCALARTransformed y value in world coordinates corresponding to y index of matrix.
pltr_data
	  (PLPointerA pointer to additional data that is passed as an
	  argument to PLplot routines that potentially could use the pltr0
	  callback (i.e., plcont, plimagefr, plshade,
	  plshades, and plvect); which then internally pass that argument on
	  to this callback.
This function is not used in any of our C examples.