Hi sfepy development team!

I try to probe the Cauchy stress of my FEM model. But errors occurred when defining the evaluation of the problem.

The full exception went like:

Traceback (most recent call last):
File "D:\ProgramFiles\Anaconda3\envs\FEM_39\lib\site-packages\sfepy\base\base.py", line 556, in getitem
ii = self.names.index(ii)
ValueError: 'ii' is not in list

However, I have defined the integral ii in the code. The full code is listed below:

from __future__ import absolute_import
import numpy as np
import pandas as pd
from sfepy.base.base import IndexedStruct
from sfepy.discrete import (FieldVariable, Material, Integral, Function, Equation, Equations, Problem)
from sfepy.discrete.conditions import Conditions, EssentialBC
from sfepy.discrete.fem import Mesh, FEDomain, Field
from sfepy.mechanics.matcoefs import stiffness_from_youngpoisson
from sfepy.solvers.ls import ScipyDirect
from sfepy.solvers.nls import Newton
from sfepy.terms import Term
from sfepy.base.base import Struct
from sfepy.postprocess.probes_vtk import Probe
from six.moves import range

hf = 1
wf = 2
hr = 5
wr = 1
hs = 1
ws = 6
theta = 0.25 * np.pi
span_len = 2
p = -0.5 * 28.14 / (wf + (hr + hs) / np.tan(theta) + ws * 0.5)  


def get_bearing_point(coors, domain=None):
    coord_df = pd.DataFrame(coors)
    bottom_coord = coord_df[(coord_df[2] == coord_df[2].min()) & (coord_df[1] == coord_df[1].min())]  # 梁端底面
    min_x = bottom_coord[0].min()
    max_x = bottom_coord[0].max()
    x_1_4 = (max_x - min_x) / 4 + min_x
    x_3_4 = 3 * (max_x - min_x) / 4 + min_x
    bearing_point_1 = bottom_coord[abs(bottom_coord[0] - x_1_4) < 0.5]
    bearing_point_2 = bottom_coord[abs(bottom_coord[0] - x_3_4) < 0.5]
    flag = np.array(
        list(set(
            list(bearing_point_1.index) + list(bearing_point_2.index)
        ))
    )
    return flag


def linear_compress(ts, coor, pressure, mode=None, **kwargs):
    if mode == 'qp':
        val = np.tile(-1 * pressure, (coor.shape[0], 1, 1))

        return {'val': val}


pressure = Function('linear_compress', linear_compress, extra_args={'pressure': p})

functions = {
    'get_bearing_point': (get_bearing_point,)
}

mesh = Mesh.from_file('box_girder.vtk')

domain = FEDomain('domain', mesh)

bounding_box = domain.get_mesh_bounding_box()
min_y, max_y = bounding_box[:, 1]
min_z, max_z = bounding_box[:, 2]
eps_y = 1e-8 * (max_y - min_y)
eps_z = 1e-8 * (max_z - min_z)

bearing = domain.create_region('bearing', 'vertices by get_bearing_point')  # 梁端固定支座
bearing = domain.create_region('bearing', 'vertices in y < %.10f' % (min_y + eps_y), 'facet')
deck = domain.create_region('deck', 'vertices in z > %.10f' % (max_z - eps_z), 'facet')  # 梁顶面
girder = domain.create_region('girder', 'all')

field = Field.from_args('fu', np.float64, 'vector', girder, approx_order=2)
u = FieldVariable('u', 'unknown', field)
v = FieldVariable('v', 'test', field, primary_var_name='u')

m = Material('m', D=stiffness_from_youngpoisson(3, 3.5e10, 0.2))
f = Material('f', val=[[0], [0], [-23520]])
load = Material('load', function=pressure)

integral = Integral('ii', order=3)

t1 = Term.new('dw_lin_elastic(m.D, v, u)', integral, girder, m=m, v=v, u=u)  # 弹性能积分项
t2 = Term.new('dw_volume_lvf(f.val, v)', integral, girder, f=f, v=v)  # 体积力积分项
t3 = Term.new('dw_surface_ltr(load.val, v)', integral, deck, load=load, v=v)  # 面力积分项

eq = Equation('balance', t1 - t2 - t3)
eqs = Equations([eq])

fix_u = EssentialBC('fix_u', bearing, {'u.all': 0.0})

ls = ScipyDirect({})
nls_status = IndexedStruct()
nls = Newton({'i_max': 1, 'eps_a': 1e-10}, lin_solver=ls, status=nls_status)

pb = Problem('elasticity', equations=eqs)
pb.save_regions_as_groups('regions')

pb.set_bcs(ebcs=Conditions([fix_u]))
pb.set_solver(nls)

status = IndexedStruct()
vec = pb.solve(status=status)

print('Nonlinear solver status:\n', nls_status)
print('Stationary solver status:\n', status)

pb.save_state('linear_elasticity.vtk', vec)


out = {}  
stress = pb.evaluate('ev_cauchy_stress.ii.girder(m.D, u)', mode='evaluate') 
		

			out['cauchy_stress'] = Struct(name='output_data', mode='cell', data=stress, dofs=None)
		

		

			
		

Besides the above question, I wonder if there is any tutorial that shows how to write postprocess code interactively.  I would greatly appreciate a full example from problem defining to postprocessing with coding style shown in this page Tutorial — SfePy version: 2023.1+git.fdee68c7 documentation.

By the way, the above problem was also subjected as issue#985 on GitHub. Evaluation failed · Issue #985 · sfepy/sfepy (github.com) I would greatly appreciate your support of any kind.