Operator
- class devito.operator.operator.Operator(expressions, **kwargs)[source]
Generate, JIT-compile and run C code starting from an ordered sequence of symbolic expressions.
- Parameters
expressions (expr-like or list or expr-like) – The (list of) expression(s) defining the Operator computation.
**kwargs –
- namestr
Name of the Operator, defaults to “Kernel”.
- subsdict
Symbolic substitutions to be applied to
expressions
.
- optstr
The performance optimization level. Defaults to
configuration['opt']
.
- languagestr
The target language for shared-memory parallelism. Defaults to
configuration['language']
.
- platformstr
The architecture the code is generated for. Defaults to
configuration['platform']
.
- compilerstr
The backend compiler used to jit-compile the generated code. Defaults to
configuration['compiler']
.
Examples
The following Operator implements a trivial time-marching method that adds 1 to every grid point in
u
at every timestep.>>> from devito import Eq, Grid, TimeFunction, Operator >>> grid = Grid(shape=(4, 4)) >>> u = TimeFunction(name='u', grid=grid) >>> op = Operator(Eq(u.forward, u + 1))
Multiple expressions can be supplied, and there is no limit to the number of expressions in an Operator.
>>> v = TimeFunction(name='v', grid=grid) >>> op = Operator([Eq(u.forward, u + 1), ... Eq(v.forward, v + 1)])
Simple boundary conditions can be imposed easily exploiting the “indexed notation” for Functions/TimeFunctions.
>>> t = grid.stepping_dim >>> x, y = grid.dimensions >>> op = Operator([Eq(u.forward, u + 1), ... Eq(u[t+1, x, 0], 0), ... Eq(u[t+1, x, 2], 0), ... Eq(u[t+1, 0, y], 0), ... Eq(u[t+1, 2, y], 0)])
A semantically equivalent computation can be expressed exploiting SubDomains.
>>> u.data[:] = 0 >>> op = Operator(Eq(u.forward, u + 1, subdomain=grid.interior))
By specifying a SubDomain, the Operator constrains the execution of an expression to a certain sub-region within the computational domain. Ad-hoc SubDomains can also be created in application code – refer to the SubDomain documentation for more info.
Advanced boundary conditions can be expressed leveraging SubDomain and SubDimension.
Tensor contractions are supported, but with one caveat: in case of MPI execution, any global reductions along an MPI-distributed Dimension should be handled explicitly in user code. The following example shows how to implement the matrix-vector multiplication
Av = b
(inducing a reduction alongy
).>>> from devito import Inc, Function >>> A = Function(name='A', grid=grid) >>> v = Function(name='v', shape=(3,), dimensions=(y,)) >>> b = Function(name='b', shape=(3,), dimensions=(x,)) >>> op = Operator(Inc(b, A*v))
Dense and sparse computation may be present within the same Operator. In the following example, interpolation is used to approximate the value of four sparse points placed at the center of the four quadrants at the grid corners.
>>> import numpy as np >>> from devito import SparseFunction >>> grid = Grid(shape=(4, 4), extent=(3.0, 3.0)) >>> f = Function(name='f', grid=grid) >>> coordinates = np.array([(0.5, 0.5), (0.5, 2.5), (2.5, 0.5), (2.5, 2.5)]) >>> sf = SparseFunction(name='sf', grid=grid, npoint=4, coordinates=coordinates) >>> op = Operator([Eq(f, f + 1)] + sf.interpolate(f))
The iteration direction is automatically detected by the Devito compiler. Below, the Operator runs from
time_M
(maximum point in the time dimension) down totime_m
(minimum point in the time dimension), as opposed to all of the examples seen so far, in which the execution along time proceeds fromtime_m
totime_M
through unit-step increments.>>> op = Operator(Eq(u.backward, u + 1))
Loop-level optimisations, including SIMD vectorisation and OpenMP parallelism, are automatically discovered and handled by the Devito compiler. For more information, refer to the relevant documentation.
- apply(**kwargs)[source]
Execute the Operator.
With no arguments provided, the Operator runs using the data carried by the objects appearing in the input expressions – these are referred to as the “default arguments”.
Optionally, any of the Operator default arguments may be replaced by passing suitable key-value arguments. Given
apply(k=v, ...)
,(k, v)
may be used to:replace a Constant. In this case,
k
is the name of the Constant,v
is either a Constant or a scalar value.replace a Function (SparseFunction). Here,
k
is the name of the Function,v
is either a Function or a numpy.ndarray.alter the iteration interval along a Dimension. Consider a generic Dimension
d
iterated over by the Operator. By default, the Operator runs over all iterations within the compact interval[d_m, d_M]
, whered_m
andd_M
are, respectively, the smallest and largest integers not causing out-of-bounds memory accesses (for the Grid Dimensions, this typically implies iterating over the entire physical domain). So nowk
can be eitherd_m
ord_M
, whilev
is an integer value.
Examples
Consider the following Operator
>>> from devito import Eq, Grid, TimeFunction, Operator >>> grid = Grid(shape=(3, 3)) >>> u = TimeFunction(name='u', grid=grid, save=3) >>> op = Operator(Eq(u.forward, u + 1))
The Operator is run by calling
apply
>>> summary = op.apply()
The variable
summary
contains information about runtime performance. As no key-value parameters are specified, the Operator runs with its default arguments, namelyu=u, x_m=0, x_M=2, y_m=0, y_M=2, time_m=0, time_M=1
.At this point, the same Operator can be used for a completely different run, for example
>>> u2 = TimeFunction(name='u', grid=grid, save=5) >>> summary = op.apply(u=u2, x_m=1, y_M=1)
Now, the Operator will run with a different set of arguments, namely
u=u2, x_m=1, x_M=2, y_m=0, y_M=1, time_m=0, time_M=3
.To run an Operator that only uses buffered TimeFunctions, the maximum iteration point along the time dimension must be explicitly specified (otherwise, the Operator wouldn’t know how many iterations to run).
>>> u3 = TimeFunction(name='u', grid=grid) >>> op = Operator(Eq(u3.forward, u3 + 1)) >>> summary = op.apply(time_M=10)
- ccode
- property cfunction
The JIT-compiled C function as a ctypes.FuncPtr object.
- cinterface(force=False)[source]
Generate two files under the prescribed temporary directory:
X.c (or X.cpp): the code generated for this Operator;
X.h: an header file representing the interface of X.c.
Where X=self.name.
- Parameters
force (bool, optional) – Overwrite any existing files. Defaults to False.
- dimensions
- input
- objects
- reads
- temporaries
- writes