Increased performance of tau methods (#491)

Author: brownbaerchen

pySDC/helpers/spectral_helper.py

@@ -1178,30 +1178,36 @@ def put_BCs_in_matrix(self, A):
     def put_BCs_in_rhs_hat(self, rhs_hat):
         """
         Put the BCs in the right hand side in spectral space for solving.
-        This function needs no transforms.
+        This function needs no transforms and caches a mask for faster subsequent use.
 
         Args:
             rhs_hat: Right hand side in spectral space
 
         Returns:
             rhs in spectral space with BCs
         """
-        ndim = self.ndim
-
-        for axis in range(ndim):
-            for bc in self.full_BCs:
-                slices = (
-                    [slice(0, self.init[0][i + 1]) for i in range(axis)]
-                    + [bc['line']]
-                    + [slice(0, self.init[0][i + 1]) for i in range(axis + 1, len(self.axes))]
-                )
-                if axis == bc['axis']:
-                    _slice = [self.index(bc['equation'])] + slices
-                    N = self.axes[axis].N
-                    if (N + bc['line']) % N in self.xp.arange(N)[self.local_slice[axis]]:
-                        _slice[axis + 1] -= self.local_slice[axis].start
-                        rhs_hat[(*_slice,)] = 0
-
+        if not hasattr(self, '_rhs_hat_zero_mask'):
+            """
+            Generate a mask where we need to set values in the rhs in spectral space to zero, such that can replace them
+            by the boundary conditions. The mask is then cached.
+            """
+            self._rhs_hat_zero_mask = self.xp.zeros(shape=rhs_hat.shape, dtype=bool)
+
+            for axis in range(self.ndim):
+                for bc in self.full_BCs:
+                    slices = (
+                        [slice(0, self.init[0][i + 1]) for i in range(axis)]
+                        + [bc['line']]
+                        + [slice(0, self.init[0][i + 1]) for i in range(axis + 1, len(self.axes))]
+                    )
+                    if axis == bc['axis']:
+                        _slice = [self.index(bc['equation'])] + slices
+                        N = self.axes[axis].N
+                        if (N + bc['line']) % N in self.xp.arange(N)[self.local_slice[axis]]:
+                            _slice[axis + 1] -= self.local_slice[axis].start
+                            self._rhs_hat_zero_mask[(*_slice,)] = True
+
+        rhs_hat[self._rhs_hat_zero_mask] = 0
         return rhs_hat + self.rhs_BCs_hat
 
     def put_BCs_in_rhs(self, rhs):
@@ -1347,18 +1353,22 @@ def get_fft(self, axes=None, direction='object', padding=None, shape=None):
                 elif direction == 'object':
                     self.fft_cache[key] = None
             else:
-                from mpi4py_fft import PFFT
-
-                _fft = PFFT(
-                    comm=self.comm,
-                    shape=shape,
-                    axes=sorted(axes),
-                    dtype='D',
-                    collapse=False,
-                    backend=self.fft_backend,
-                    comm_backend=self.fft_comm_backend,
-                    padding=padding,
-                )
+                if direction == 'object':
+                    from mpi4py_fft import PFFT
+
+                    _fft = PFFT(
+                        comm=self.comm,
+                        shape=shape,
+                        axes=sorted(axes),
+                        dtype='D',
+                        collapse=False,
+                        backend=self.fft_backend,
+                        comm_backend=self.fft_comm_backend,
+                        padding=padding,
+                    )
+                else:
+                    _fft = self.get_fft(axes=axes, direction='object', padding=padding, shape=shape)
+
                 if direction == 'forward':
                     self.fft_cache[key] = _fft.forward
                 elif direction == 'backward':