PhiFlow Fluid usage with PyTorch about phiflow

[holl-]

Hi Nikolai,

Thanks for your feedback!
Unfortunately we don't have anyone with a lot of experience in PyTorch in our group, so we don't yet have advanced tests.

I'll look into the error shortly and post a fix.

Best,
Philipp

[holl-]

I have fixed this issue in the develop branch. The following script now runs until the last line.

from phi.torch.flow import *
from torch.utils.data import TensorDataset, DataLoader

inputs = torch.rand(1000, 10, 10, 1)
targets = torch.rand(1000, 10, 10, 1)
dataset = TensorDataset(inputs, targets)
dataloader = DataLoader(dataset, batch_size=10)
domain = Domain([10, 10], boundaries=PERIODIC)
sz = domain.staggered_grid(0).staggered_tensor().shape
initial_velocity = torch.zeros(*sz)
initial_velocity = initial_velocity.expand(10, *initial_velocity.shape[1:])
velocity = torch.nn.Parameter(initial_velocity)
optimizer = torch.optim.Adam([velocity], lr=1e-3)
for epoch in range(10):
    for batch_index, (inputs, targets) in enumerate(dataloader):
        optimizer.zero_grad()
        domain = Domain([10, 10], boundaries=PERIODIC)
        fluid = Fluid(domain, batch_size=10, density=inputs, velocity=velocity)
        density = advect.semi_lagrangian(fluid.density, fluid.velocity, dt=1)
        density = diffuse(density, 1 * 0.1, substeps=1)
        loss = math.l2_loss(density.data - targets)
        loss.backward()
        optimizer.step()

The optimizer.step() still complains that
more than one element of the written-to tensor refers to a single memory location. Please clone() the tensor before performing the operation.
It sounds to me like the problem lies in the setup. Can you confirm this?

Note that Fluid.density is read-only. Use fluid.copied_with(density=new_density) to make an altered copy.

[ne3x7]

Thank you for such a prompt response. Indeed, Fluid object is created correctly now. I also confirm that the problem with optimizer lies in the setup, to be precise, in the line initial_velocity = initial_velocity.expand(10, *initial_velocity.shape[1:]). This operation should be done at each step when creating Fluid object. I am now closing the issue, thank you again!