MAKE PARAMS COMPATIBLE

   char *mk_xxx_compatible_params(examples *exams, 
                                  ivec *in_att_nums,
                                  ivec *out_att_nums,
                                  char *params)

An optional function.  Suppose the user
changes the set of examples to be used, or
the set of input attributes, or the set of
output attributes. This may mean the
parameters are now
invalid. mk_xxx_compatible_params checks to
see if the parameters are still compatible;
if so, it returns NULL; if they are
incompatible, it returns a new set of
suitable parameters.

If this function is unimplemented, the
high-level code will assume that any change
in the examples or the att_nums renders the
parameters invalid, and will revert to
default parameters.