Accessing entries of Global size matrix

General
2

Considering something along the lines of

from fenics import *
import numpy as np

# Create mesh and function space
mesh = UnitSquareMesh(2, 2)
V = FunctionSpace(mesh, 'P', 1)

# Define trial and test functions
u = TrialFunction(V)
v = TestFunction(V)
a = inner(grad(u), grad(v)) * dx
A = PETScMatrix()
assemble(a, tensor=A)

def print_entries(entries):
    # DO NOT DO THIS IN AN ACTUAL CODE. You can use A.get instead
    AM = np.array(A.array())
    for entry in entries:
        print(f"Before: A[{entry[0], entry[1]}] = {AM[entry[0], entry[1]]}")

print("Before")
print_entries([(0, 0), (0, 1), (1, 0), (1, 1)])

A.set([[2.0, 3.0], [4.0, 5.0]], [0, 1], [0, 1])
A.apply("insert")

print("After")
print_entries([(0, 0), (0, 1), (1, 0), (1, 1)])

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