The first formulation of QM was done by heisenberg using matrix mechanics. This was quite complicated. Schrödinger then formuled his wave mechanics. This was easier. Dirac unified them by using his dirac notation.
The first formulation of QM was done by heisenberg using matrix mechanics. This was quite complicated. Schrödinger then formuled his wave mechanics. This was easier. Dirac unified them by using his dirac notation.