For the second time I made a trip out to my daughter in Rosenberg (southwest of Houston) from San Antonio. I didn't pay close attention the first time and it took me on a different route when I left. This time I paid a bit more attention and it took me the same way. I don't know that the second route is shorter but it is at least as fast as there are no stops.
I am just curious as to why it doesn't choose the same route both ways. Next time I will know the roads and make sure I don't turn off and go the direction I don't want to go.
I almost always check my GPS routes to make sure I agree with what it is trying to do. Sometimes I have to stick in a Via to avoid going through a town, or section of road I know I don't like. They are great for what they are, but to blindly follow one when you know orienteering can lead to frustration.
I have a some experience with routing algorithms for connecting integrated circuits. It is a complex problem and small things can effect the solution. One obvious one is one way streets but also the exit from a highway versus the on ramp going the other direction may have different "costs" to the algorithm. Or as 2 wheel said, right versus left turns. In a maze search algorithm, when straight ahead is not a good solution it might first try right instead of left at any given intersection. Giving a different solution for a different direction.