Most of us at one time or another have been confronted with some music, which is much too hard for us to play. Here is a 7-step process, which can help you learn such a passage in a smaller amount of time:
         ( I learned this from Bass Viol virtuoso Roger Ruggieri)

1. Through experimentation, decide on the best possible fingering, picking pattern and fingerboard position.
2. Rewrite the line without any rhythms so you can focus in on the notes.
3. Play with dotted rhythms, long, short, long, short, etc.
4. Reverse the dotted rhythms, short, long, etc.
5. Play the line in triplets.
6. Start the triplets on the second note.
7. Start the triplets on the third note.
     
By moving the accents around, you are gradually removing all the obstacles that exist between each pair of notes. With the dotted rhythms you are playing each pair of notes much faster than you could possibly play the whole line. If after going through this process you still have trouble with the original, repeat this process on the line every day until you get it. Don't forget to use a metronome.