Finishing touches for schint()

Your routine schint() is almost complete. It requires only three finishing touches, that you double-check one part of its functionality, that you improve its reliability and that you improve its efficiency.

In terms of functionality, as parts of this problem set begin to use Psiout[], it is important to be sure that all values are entered into the array. (See Problem 2.1.)

As discussed in lab, the final value of Psi which schint() outputs sometimes overflows. Problem 2.2 deals with this issue of reliability.

Most of the calls which your program will make to schint() are to find the energies. These calls use only the final returned value *Psi and not the full array of values Psiout[]. Problem 2.3 deals with this inefficiency using ``NULL'' pointers, an elegant solution common in C.