This may not strictly be a fenics question, but suppose I run a time dependent problem, of the sort: output = XDMFFile("out.xdmf") for n in range(nmax): # computational steps output.write(u,t) output.close() If I then read this in with paraview, it’s all as expected. But I was wondering how …

write saves the data at the vertices, efficiently projecting the solution to a CG-1 function space. write_checkpoint saves the data with the appropriate function space, and can therefore be read into dolfin again, to the appropriate function space. You are not saving multiple time steps to your fi…

Two follow up questions: If I am fine reading the data in with Paraview (or some similar program), is there any reason I should stop using write? I am still struggling to get the suggested approach working. Here is what a minimal example: nx = ny = 8 mesh = UnitSquareMesh(nx, ny) V = FunctionSpa…

Yes, that now works. One question: output in generated with write_checkpoint now doesn’t seem to be readable by Paraview. Is this to be expected, or is there some way to make it compatible with both?

then your paraview is out of data. You Need to use Paraview >=5.5.0

is there a way with the method read_checkpoint to read the actual time of the i_th time step ? let’s say for example you want to recreate the exact same xdmf file ? from fenics import * file_in = XDMFFile("in.xdmf") file_out = XDMFFile("out.xdmf") mesh = Mesh() file_in.read(mesh) V = FunctionSpa…

As you can see from the documentation: https://fenicsproject.org/docs/dolfin/latest/cpp/de/d71/classdolfin_1_1XDMFFile.html#aa86a07b92188a2da32d1a0e128106c91 That is not possible, as read_checpoint only takes in a counter.

I’m using 5.7.0, and I’m seeing that some of the fields are listed as partial. The consequence seems to be that I don’t have the field at every time at which I performed a write_checkpoint. See attached screen capture. [31%20PM]

Are you using the append functionality. I see none of the issues with the following code: from dolfin import * nx = ny = 8 mesh = UnitSquareMesh(nx, ny) V = FunctionSpace(mesh, 'P', 1) alpha = 3; beta = 1.2 f = Expression('1 + x[0]*x[0] + alpha*x[1]*x[1] + beta*t', degree=2, alpha=alpha, beta=bet…

Yeah, my mistake is I was appending to an existing file. Once I put False in the first call, it cleared up.

Hello Jorgen, is there still any way to read the data back in when they were already written using write instead of write_checkpoint?

No, you cannot read in data written with XDMFFile.write.

Loading xdmf data back in

I/O

dokken February 15, 2022, 9:02am 22

See for instance: Interpolation of Indexed Functions of Mixed Elements - #2 by dokken

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Loading xdmf data back in

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