  The standard quantum mechanics assumes Schr\"odinger equation for regular
evolution and wave function collapse for measurement. As shown in this paper,
only particular collapse equation can continuously transition to Schr\"odinge
equation. The collapse equation also adds some restriction to the
preferred-basis. Under the assumptions that the preferred-basis depends on the
whole system Hamiltonian but is not affected by the weights of the basis
functions in the system wave function, a unique set of determination equations
of the basis functions is derived from the collapse equation. The second order
time derivative of the wave function is continuous at the end of the collapse.
To make the derivative continuous at the beginning of the collapse, it is
proved that the collapse equation has to contain a cyclic function with period
twice the duration of the collapse, which leads to conditioned alternating
Schr\"odinger evolution and collapse of equal duration.
