Exact diagonalization using Laczos method

This is the simple example for using cytnx with ED to calculate 1D Transverse field ising model:

H = -[s]SzSz - (1-[s])Sx

Cytnx library:

Cytnx

Results:

The (2nd) energy gap with different system size L that shows the avoid level crossing:

Implementations:

* ed_ising.py 
    This one using the overload of matvec interface directly, memory efficient

* ed_ising_mve.py
    This one store all the elements when calling pre-construct, and use openmp to accelerate. performance efficient

Developer:

Kai-Hsin Wu