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from petsc4py import PETSc as Pet

import numpy as np

import scipy.sparse

A = np.array([[2,0,0,0],[0,2,0,0],[0,0,2,0],[0,0,0,2]])

print A

print A.shape

A_csr = scipy.sparse.csr_matrix(A)

A_petsc = Pet.Mat().createAIJ(size=A_csr.shape,

csr = (A_csr.indptr, A_csr.indices, A_csr.data))

x,b = A_petsc.getVecs()

b.set(1)

print b.getArray()

# create linear solver

ksp = Pet.KSP()

ksp.create(Pet.COMM_WORLD)

ksp.setType('cg')

pc = ksp.getPC()

pc.setType(pc.Type.GAMG)

ksp.setOperators(A_petsc)

ksp.solve(b,x)

print x.getArray()

# and incomplete Cholesky

#ksp.getPC().setType('icc')

# obtain sol & rhs vectors

#x, b = A.createVecs()

#x.set(0)

#b.set(1)

# and next solve

#ksp.setOperators(A)

#ksp.setFromOptions()

#ksp.solve(b, x)