TypeError: 'SumBlockedOperator' object is not subscriptable

Bempp
1

Hello all,
with BEMpp 0.3.1, when trying the snippets of figures 9 (preconditioned EFIE) and 13 (MFIE) extract from the 2017 amazing paper Redirecting.

import numpy as np
import bempp.api
from bempp.api.operators.boundary import maxwell
from bempp.api.operators.boundary import sparse
k=2
grid=bempp.api.shapes.cube(h=0.2)

def incident_field(x):
    return np.array([np.exp(1j*k*x[2]),0.*x[2],0.*x[2]])

@bempp.api.complex_callable
def tangential_trace(x,n,domain_index,result):
    result[:]=np.cross(np.array([1.,0.,0.]),n)*np.exp(1j*k*x[2])

#multitrace=maxwell.multitrace_operator(grid,k) # Lead to error when calculating E1
multitrace=maxwell.multitrace_operator(grid,k,space_type='all_rwg')
#identity=sparse.multitrace_identity(multitrace),spaces='maxwell') # doesn't work
identity=sparse.multitrace_identity(multitrace)
calderon=0.5*identity-multitrace

op=-calderon[0,0]
rhs=bempp.api.GridFunction(calderon.domain_spaces[0],fun=tangential_trace,dual_space=calderon.dual_to_range_spaces[0])
sol,info=bempp.api.linalg.gmres(op,rhs,use_strong_form=True)

we got error:

bempp:HOST:INFO: Created grid with id b3e09375-25df-4aa4-bc2d-82d2d4927082. Elements: 2400. Edges: 3600. Vertices: 1202

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[4], line 21
     18 identity=sparse.multitrace_identity(multitrace)
     19 calderon=0.5*identity-multitrace
---> 21 op=-calderon[0,0]
     22 rhs=bempp.api.GridFunction(calderon.domain_spaces[0],fun=tangential_trace,dual_space=calderon.dual_to_range_spaces[0])
     23 sol,info=bempp.api.linalg.gmres(op,rhs,use_strong_form=True)

TypeError: 'SumBlockedOperator' object is not subscriptable

Any idea?

Thanks in advance for help,

Gérard

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