It is usually said that there are different formulations of QM, for example historically there was Schrodinger's (wave mechanics), and Heisenberg's (matrix mechanics), then Dirac's (which showed they are equivalent)
Since they are all physically equivalent I have a few questions:
1-Is Dirac's formulations considered more fundamental in the sense that it can be reduced to one of the 1st two?
2-I also hear about the path integral and density matrices, are they another formulations?
3-Are there more formulations less known to undergraduate students but known by researchers because they are technically advanced?