... index.

It appears a bit heavy handed with all of the casts to long ints, but there were some problems of improper type promotion encountered during development.

... vdoub.

This ability to operate on the hdr of vdoub clarified the meaning of inheritance for me since a VMatrix is really just a virtual vector with some extra functionality. It also shows why the hdr must be protected rather than private in vdoub.

... functions.

If you force a zero division in this routine, VAX CC will cause a print of the function call sequence to the error output stream