Commit 2e42e5ba authored by Martin Bauer's avatar Martin Bauer
Browse files

Generalized assignment_from_stencil

- relative application of stencil by passing in field accesses
- documentation + doctest
parent aa2c89d8
......@@ -15,11 +15,11 @@ def print_assignment_latex(printer, expr):
"""sympy cannot print Assignments as Latex. Thus, this function is added to the sympy Latex printer"""
printed_lhs = printer.doprint(expr.lhs)
printed_rhs = printer.doprint(expr.rhs)
return "{printed_lhs} \leftarrow {printed_rhs}".format(printed_lhs=printed_lhs, printed_rhs=printed_rhs)
return r"{printed_lhs} \leftarrow {printed_rhs}".format(printed_lhs=printed_lhs, printed_rhs=printed_rhs)
def assignment_str(assignment):
return "{lhs} ← {rhs}".format(lhs=assignment.lhs, rhs=assignment.rhs)
return r"{lhs} ← {rhs}".format(lhs=assignment.lhs, rhs=assignment.rhs)
if Assignment:
......@@ -51,15 +51,64 @@ else:
_print_Assignment = print_assignment_latex
def assignment_from_stencil(stencil_array, input_field, output_field, normalization_factor=None):
def assignment_from_stencil(stencil_array, input_field, output_field,
normalization_factor=None, order='visual') -> Assignment:
"""Creates an assignment
stencil_array: nested list of numpy array defining the stencil weights
input_field: field or field access, defining where the stencil should be applied to
output_field: field or field access where the result is written to
normalization_factor: optional normalization factor for the stencil
order: defines how the stencil_array is interpreted. Possible values are 'visual' and 'numpy'.
For details see examples
Assignment that can be used to create a kernel
>>> import pystencils as ps
>>> f, g = ps.fields("f, g: [2D]")
>>> stencil = [[0, 2, 0],
... [3, 4, 5],
... [0, 6, 0]]
By default 'visual ordering is used - i.e. the stencil is applied as the nested lists are written down
>>> assignment_from_stencil(stencil, f, g, order='visual')
Assignment(g_C, 3*f_W + 6*f_S + 4*f_C + 2*f_N + 5*f_E)
'numpy' ordering uses the first coordinate of the stencil array for x offset, second for y offset etc.
>>> assignment_from_stencil(stencil, f, g, order='numpy')
Assignment(g_C, 2*f_W + 3*f_S + 4*f_C + 5*f_N + 6*f_E)
You can also pass field accesses to apply the stencil at an already shifted position:
>>> assignment_from_stencil(stencil, f[1, 0], g[2, 0])
Assignment(g_2E, 3*f_C + 6*f_SE + 4*f_E + 2*f_NE + 5*f_2E)
from pystencils import Field
stencil_array = np.array(stencil_array)
if order == 'visual':
stencil_array = np.swapaxes(stencil_array, 0, 1)
stencil_array = np.flip(stencil_array, axis=1)
elif order == 'numpy':
raise ValueError("'order' has to be either 'visual' or 'numpy'")
if isinstance(input_field, Field):
input_field =
if isinstance(output_field, Field):
output_field =
rhs = 0
offset = tuple(s // 2 for s in stencil_array.shape)
for index, factor in np.ndenumerate(stencil_array):
rhs += factor * input_field[tuple(i - o for i, o in zip(index, offset))]
shift = tuple(i - o for i, o in zip(index, offset))
rhs += factor * input_field.get_shifted(*shift)
if normalization_factor:
rhs *= normalization_factor
return Assignment(, rhs)
return Assignment(output_field, rhs)
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