In expressions like ``phi=I(Linv((-4*pi)*O(J(rho))));'' we think of
phi and rho as vectors of the values of the potential
and charge density
at a set of sample points
. For our Fourier representation the data in these ``vectors''
are actually stored on a three-dimensional mesh of points. We shall
call the class which represents these physics vectors the
``pvector'' class.
Appendix C contains most of the specification of the pvector class, along with a main program to test it. This section will teach you the basics of making such a class by having you complete its specification.