You can declare your own stencil operators using the macro
BZ_DECLARE_STENCIL_OPERATOR1
. For example, here is the
declaration of Laplacian2D
:
BZ_DECLARE_STENCIL_OPERATOR1(Laplacian2D, A)
return -4*A(0,0) + A(-1,0) + A(1,0) + A(0,-1) + A(0,1);
BZ_END_STENCIL_OPERATOR
To declare a stencil operator on 3 operands, use
the macro BZ_DECLARE_STENCIL_OPERATOR3. Here is
the declaration of div
:
BZ_DECLARE_STENCIL_OPERATOR3(div,vx,vy,vz)
return central12(vx,firstDim) + central12(vy,secondDim)
+ central12(vz,thirdDim);
BZ_END_STENCIL_OPERATOR
The macros aren't magical; they just declare an inline
template function with the names and arguments you specify.
For example, the declaration of div
could also
be written
template<class T>
inline typename T::T_numtype div(T& vx, T& vy, T& vz)
{
return central12(vx,firstDim) + central12(vy,secondDim)
+ central12(vz,thirdDim);
}
The template parameter T
is an iterator type for
arrays.
You are encouraged to use the macros when possible, because
it is possible the implementation could be changed in the
future.
To declare a difference operator, use this syntax:
BZ_DECLARE_DIFF(central12,A) {
return A.shift(1,dim) - A.shift(-1,dim);
}
The method shift(offset,dim)
retrieves the element at
offset
in dimension dim
.
Stencil operator declarations cannot occur inside a function. If
declared inside a class, they are scoped by the class.