Andrew Sarangan wrote:
Most of the software out there will compute a flight based on the
user's route, time of departure and altitude. This is a fairly
straight forward task which could be done without a computer, as has
been the case for decades.

What I am looking for is the reverse. Given a destination, aircraft
type and a window of travel time (which could be a couple of days),
the software should come up with the best altitude, route and time of
departure. It should consider forecasted winds aloft, frontal
positions, icing potentials, turbulence and thunderstorms. The user
should be able to attach numeric weights to indicate the level of
importance to each factor. In other words, it should be a minimization
software considering a variety of decision matrix. At present I do
this by recomputing the flight for each scenario. This does get very
cumbersome, and is best done with an automated algorithm. If such a
thing exists, I would like to hear opinions.

The algorithm you are looking for is known as Djikstra's Algorithm, for
finding the optimum path through a network. You can google for it if
you're not familiar.

The network could be the nodes and airways of the airway system, but
this limits the available solutions to airways.

Winds, altitude requirements, leg lengths are relatively easily
accounted for. The trick is assigning costs to factors like frontal
penetrations, icing risk and thunderstorm risk.