If one imports say a C Major scale in Guitar Pro, it auto calculates the fret numbers/strings.
Does anyone know by what logic it does this (since there are many possible ways to play a C major scale on a guitar)? Why one way and not another?
If you are wondering on how to get a suitable/optimal fingering position, there are some existing research that develop such algorithms.
For Guitar fingers position, take a look at the following paper: http://www.csc.kth.se/utbildning/kth/kurser/DD143X/dkand13/Group7Anders/final/Vladimir.Grozman.Christopher.Norman.report.pdf
The algorithm is graph-based where each node represents few elements such as String Number, Fret Number, Note duration, etc. And it tries to find a solution that will minimize the cost of transition between the notes.
For Piano fingers position, take a look at the following paper: http://ijcai.org/papers07/Papers/IJCAI07-469.pdf
It is based on a statistical model called Hidden Markov Model.