Basic queries from the fenics book, chapter 1, Set #2

[bhaveshshrimali]

@Golam

The following does not work, I receive runtime error

1a.)
u_nodal_values = u.vector()
u_array = u_nodal_values.get_local()
print(u_array)

Can you supply a minimal example ? This should work

import numpy as np
from dolfin import *
V = FunctionSpace(UnitSquareMesh(10, 10), "CG", 1) 
u = Function(V)
u.vector()[:] = np.arange(V.dim())
print(u.vector().get_local())

@Golam

File('poisson/u_array') << u_array

It’s a numpy array. You can simply use numpy.savetxt() or for larger arrays numpy.save() or pickle or even h5py.

@Golam

how to relate the u_array to the global mesh coordinates number?

See this

@Golam

How lok look for documentation in a terminal

from dolfin import *
help(Mesh)

@Golam

How the degree can be 1 in the Expression object with exponential function?

I may have to check, but you can try and increase the degree to see what happens

@Golam

Why there is an error in print statement

print(r"sigma = %8g: max deviation = %8g"%(sigma, dev)) #this is a python question

@Golam

How to plot multiple figures like in matlab, figure(1),…figure(n). When I run in a linux terminal, I have to close one plot to see the next one

You can look at examples in matplotlib. Basically create subplots, and then traverse the axes list. See this for a minimal example

@Golam

Where to look for the elevate attribute? I get error like this.
AttributeError: ‘TriContourSet’ object has no attribute ‘elevate’

Again, I would suggest create a matplotlib.pyplot figure/axis and then play around with the view_angles

@Golam

I suppose the following is intended to show the summary of variables in a terminal, but it does not show

See this. Although it’s old, but still should give you what you want.

I know google results for functions will more often than not lead you to older releases of dolfin but searching the documentation and this forum should lead you to answers with most of the basic questions.