Parameter: ifast

Definition

It is a key control flag, used to choose the efficient algorithms for the calculation of the operator trace.

Type

Integer

Default value

1

Component

Only for the MANJUSHAKA component.

Behavior

According to the ifast parameter, the quantum impurity solvers will choose suitable algorithm to evaluate the operator trace.

There are three possible values for ifast parameter so far:

• ifast = 1, the divide-and-conquer algorithm will be used. At this time, you have to adjust npart parameter carefully to obtain good computational efficiency. (see npart parameter as well)

• ifast = 2, the classic time evolution algorithm will be used.

• ifast = 3, the skip listing algorithm will be used.

All in all, now only ifast = 1 is valid. Even you set ifast = 2 or ifast = 3, the MANJUSHAKA code will still use the divide-and-conquer algorithm to calculate the operator trace.

Comment

In the MANJUSHAKA code, the Lazy trace evaluation trick^[1] is always used. As for the divide-and-conquer algorithm and the classic time evolution algorithm, please refer to Emanuel Gull's PhD thesis.

Reference