Added block2 MPO example.

docs/plot-generators/block2-plots.py

@@ -0,0 +1,38 @@
+import numpy as np
+from timeit import default_timer as timer
+from pyblock2.driver.core import DMRGDriver, SymmetryTypes, MPOAlgorithmTypes
+
+L = 100
+N = L
+TWOSZ = 0
+
+driver = DMRGDriver(scratch="./tmp", symm_type=SymmetryTypes.SZ, n_threads=4)
+driver.initialize_system(n_sites=L, n_elec=N, spin=TWOSZ)
+
+t = 1
+U = 4
+
+b = driver.expr_builder()
+
+epsilon = lambda k : 2 * np.cos(2 * np.pi * k / L)
+
+# Kinetic term
+for k in range(L):
+  b.add_term("cd", np.array([k, k]), -t * epsilon(k))
+  b.add_term("CD", np.array([k, k]), -t * epsilon(k))
+
+# Interaction term
+sites = np.zeros(4 * L * L * L, dtype=np.int16)
+for p in range(L):
+  for q in range(L):
+    for k in range(L):
+      b.add_term("cCDd", np.array([(p - k) % L, (q + k) % L, q, p]), U)
+
+print("Done constructing representation.")
+
+alg = MPOAlgorithmTypes.SVD | MPOAlgorithmTypes.Blocked
+# alg = MPOAlgorithmTypes.SVD | MPOAlgorithmTypes.Fast | MPOAlgorithmTypes.Blocked | MPOAlgorithmTypes.Disjoint
+start = timer()
+mpo = driver.get_mpo(b.finalize(), iprint=1, algo_type=alg)
+stop = timer()
+print(f"N = {L}, time = {stop - start}")