Re: gf.asm_generic mistake immediately after a mesh change

[Lorenzo Ferro]

Hello Konstantinos,

I've realized for this troubleshooting a simplified example, where I generate a 1D mesh corresponding to the radius of a circular section.

Then I've added the mim and I've calculated the corresponding area both analytically and numerically with asm_generic considering the axisymmetric configuration.

I removed convexes and points from the mesh with the del_convex and del_point methods and then I generated other elements on the same mesh object.

The numerical area calculation turns out to be wrong.

####### CODE START #######

import getfem as gf

import numpy as np

RoundRadius=0.01

NumberOfElements = 5

nodes = np.arange(0, RoundRadius+RoundRadius/NumberOfElements, RoundRadius/NumberOfElements)

mesh = gf.Mesh("cartesian", nodes)

im_degree = 3

mim = gf.MeshIm(mesh, im_degree)

RoundSection = np.pi*R**2

RoundSection_asm = gf.asm_generic(mim, 0, '2*pi*X' , -1)

print ("STARTING AREA CALCULATION")

print ("analitical section =", RoundSection, "VS numerical section = ", RoundSection_asm)

# Change completely the mesh

mesh.del_convex(mesh.cvid())

mesh.del_point(mesh.pid())

NumberOfElements = 10

nodes = np.arange(0, RoundRadius+RoundRadius/NumberOfElements, RoundRadius/NumberOfElements)

mesh.add_point([nodes])

for x in range(NumberOfElements):

    mesh.add_convex(gf.GeoTrans('GT_QK(1,1)'), [[nodes[x], nodes[x+1]]])

RoundSection_asm = gf.asm_generic(mim, 0, '2*pi*X' , -1)

print ("AREA CALCULATION AFTER MESH CHANGE")

print ("analytical section =", RoundSection, "VS numerical section = ", RoundSection_asm)

# Let's try to apply another mesh method

mesh.set_pts([nodes])

RoundSection_asm = gf.asm_generic(mim, 0, '2*pi*X' , -1)

print ("AREA CALCULATION AFTER MESH.SET_PTS METHOD")

print ("analytical section =", RoundSection, "VS numerical section = ", RoundSection_asm)

####### CODE FINISH#######

Thank you,

Lorenzo

Il giorno mer 20 lug 2022 alle ore 11:43 Konstantinos Poulios <logari81@googlemail.com> ha scritto:

Dear Lorenzo,

It would be very useful if you could provide a minimal test case that demonstrates this issue. Strange that md.set_time() helps updating the model correctly.

Best regards

Kostas

On Mon, Jul 18, 2022 at 4:36 PM Lorenzo Ferro <lorenzo.iron@gmail.com> wrote:

Dear All,

I'm experimenting with mesh changes (a sequence like del_convex -> del_point -> add_point -> add_convex -> set_region) and relevant MeshFEM automatic adaptation with the Python interface.

I found out that as soon as I update mesh and regions, if after that I try to run a test assembly method for example just to calculate the total area of the mesh elements (via gf.asm_generic) I achieve a completely wrong result, 

but,

after just running a Model method like "md.set_time(0.)" and then running immediately "gf.asm_generic" then I achieve the correct result!

Is this a bug? or is there some logic behind this behaviour?

Thank you,

Lorenzo