Implemented a few fixes to the FFT

jaxpm/ops.py

@@ -4,7 +4,7 @@ import jax.numpy as jnp
 import mpi4jax
 
 
-def fft3d(arr, token=None, comms=None):
+def fft3d(arr, comms=None):
     """ Computes forward FFT, note that the output is transposed
     """
     if comms is not None:
@@ -20,7 +20,7 @@ def fft3d(arr, token=None, comms=None):
     else:
         arr = arr.reshape(shape[:-1]+[nx, shape[-1] // nx])
         arr = arr.transpose([2, 1, 3, 0])  # [y, z, x]
-        arr, token = mpi4jax.alltoall(arr, comm=comms[0], token=token)
+        arr, token = mpi4jax.alltoall(arr, comm=comms[0])
         arr = arr.transpose([1, 2, 0, 3]).reshape(shape)  # Now [y, z, x]
 
     # Second FFT along x
@@ -35,15 +35,10 @@ def fft3d(arr, token=None, comms=None):
         arr = arr.transpose([1, 2, 0, 3]).reshape(shape)  # Now [z, x, y]
 
     # Third FFT along y
-    arr = jnp.fft.fft(arr)
+    return jnp.fft.fft(arr)
-
-    if comms == None:
-        return arr
-    else:
-        return arr, token
 
 
-def ifft3d(arr, token=None, comms=None):
+def ifft3d(arr, comms=None):
     """ Let's assume that the data is distributed accross x
     """
     if comms is not None:
@@ -59,7 +54,7 @@ def ifft3d(arr, token=None, comms=None):
     else:
         arr = arr.reshape(shape[:-1]+[ny, shape[-1] // ny])
         arr = arr.transpose([2, 0, 3, 1])  # Now [z, y, x]
-        arr, token = mpi4jax.alltoall(arr, comm=comms[1], token=token)
+        arr, token = mpi4jax.alltoall(arr, comm=comms[1])
         arr = arr.transpose([1, 2, 0, 3]).reshape(shape)  # Now [z,y,x]
 
     # Second FFT along x
@@ -73,22 +68,17 @@ def ifft3d(arr, token=None, comms=None):
         arr, token = mpi4jax.alltoall(arr, comm=comms[0], token=token)
         arr = arr.transpose([1, 2, 0, 3]).reshape(shape)  # Now [x,y,z]
 
-    # Third FFT along y
+    # Third FFT along z
-    arr = jnp.fft.fft(arr)
+    return jnp.fft.ifft(arr)
-
-    if comms == None:
-        return arr
-    else:
-        return arr, token
 
 
-def halo_reduce(arr, halo_size, token=None, comms=None):
+def halo_reduce(arr, halo_size, comms=None):
 
     # Perform halo exchange along x
     rank_x = comms[0].Get_rank()
     margin = arr[-2*halo_size:]
     margin, token = mpi4jax.sendrecv(margin, margin, rank_x-1, rank_x+1,
-                                     comm=comms[0], token=token)
+                                     comm=comms[0])
     arr = arr.at[:2*halo_size].add(margin)
 
     margin = arr[:2*halo_size]
@@ -108,7 +98,8 @@ def halo_reduce(arr, halo_size, token=None, comms=None):
                                      comm=comms[1], token=token)
     arr = arr.at[:, -2*halo_size:].add(margin)
 
-    return arr, token
+    return arr
+
 
 def zeros(shape, comms=None):
     """ Initialize an array of given global shape
@@ -121,3 +112,17 @@ def zeros(shape, comms=None):
     ny = comms[1].Get_size()
 
     return jnp.zeros([shape[0]//nx, shape[1]//ny]+list(shape[2:]))
+
+
+def normal(key, shape, comms=None):
+    """ Generates a normal variable for the given
+    global shape.
+    """
+    if comms is None:
+        return jax.random.normal(key, shape)
+
+    nx = comms[0].Get_size()
+    ny = comms[1].Get_size()
+
+    return jax.random.normal(key,
+                             [shape[0]//nx, shape[1]//ny]+list(shape[2:]))

scripts/test_fft3d.py

@@ -0,0 +1,61 @@
+from mpi4py import MPI
+import jax
+import jax.numpy as jnp
+import mpi4jax
+from jaxpm.ops import fft3d, ifft3d, normal
+
+# Create communicators
+world = MPI.COMM_WORLD
+rank = world.Get_rank()
+size = world.Get_size()
+
+cart_comm = MPI.COMM_WORLD.Create_cart(dims=[2, 2],
+                                       periods=[True, True])
+comms = [cart_comm.Sub([True, False]),
+         cart_comm.Sub([False, True])]
+
+if rank == 0:
+    print("Communication setup done!")
+
+
+# Setup random keys
+master_key = jax.random.PRNGKey(42)
+key = jax.random.split(master_key, size)[rank]
+
+# Size of the FFT
+N = 256
+mesh_shape = [N, N, N]
+
+# Generate a random gaussian variable for the global
+# mesh shape
+original_array = normal(key, mesh_shape, comms=comms)
+
+# Run a forward FFT
+karray = jax.jit(lambda x: fft3d(x, comms=comms))(original_array)
+rarray = jax.jit(lambda x: ifft3d(x, comms=comms))(karray)
+
+# Testing that the fft is indeed invertible
+print("I'm ", rank, abs(rarray.real - original_array).mean())
+
+
+# Testing that the FFT is actually what we expect
+total_array, token = mpi4jax.allgather(original_array, comm=comms[0])
+total_array = total_array.reshape([N, N//2, N])
+total_array, token = mpi4jax.allgather(
+    total_array.transpose([1, 0, 2]), comm=comms[1], token=token)
+total_array = total_array.reshape([N, N, N])
+total_array = total_array.transpose([1, 0, 2])
+
+total_karray, token = mpi4jax.allgather(karray, comm=comms[0], token=token)
+total_karray = total_karray.reshape([N, N//2, N])
+total_karray, token = mpi4jax.allgather(
+    total_karray.transpose([1, 0, 2]), comm=comms[1], token=token)
+total_karray = total_karray.reshape([N, N, N])
+total_karray = total_karray.transpose([1, 0, 2])
+
+print('FFT test:', rank, abs(jnp.fft.fftn(
+    total_array).transpose([2, 0, 1]) - total_karray).mean())
+
+if rank == 0:
+    print("For reference, the mean value of the fft is", jnp.abs(jnp.fft.fftn(
+        total_array)).mean())