xfunction¶
Defined in xtensor/xfunction.hpp
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template<class F, class ...CT>
class xfunction : private xt::xconst_iterable<xfunction<F, CT...>>, public xt::xsharable_expression<xfunction<F, CT...>>, private xt::xconst_accessible<xfunction<F, CT...>>, public extension::xfunction_base_t<F, CT...>¶ Multidimensional function operating on xtensor expressions.
The xfunction class implements a multidimensional function operating on xtensor expressions.
- Template Parameters
F – the function type
CT – the closure types for arguments of the function
Constructor
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template<class Func, class ...CTA, class U = std::enable_if_t<!std::is_base_of<std::decay_t<Func>, self_type>::value>>
inline xfunction(Func &&f, CTA&&... e) noexcept¶ Constructs an xfunction applying the specified function to the given arguments.
- Parameters
f – the function to apply
e – the xexpression arguments
Size and shape
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inline size_type dimension() const noexcept¶
Returns the number of dimensions of the function.
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inline const inner_shape_type &shape() const¶
Returns the shape of the xfunction.
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inline layout_type layout() const noexcept¶
Returns the layout_type of the xfunction.
Data
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inline const_reference flat(size_type i) const¶
Returns a constant reference to the element at the specified position of the underlying contiguous storage of the function.
- Parameters
index – index to underlying flat storage.
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template<class ...Args>
inline auto operator()(Args... args) const -> const_reference¶ Returns a constant reference to the element at the specified position in the function.
- Parameters
args – a list of indices specifying the position in the function. Indices must be unsigned integers, the number of indices should be equal or greater than the number of dimensions of the function.
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template<class ...Args>
inline auto unchecked(Args... args) const -> const_reference¶ Returns a constant reference to the element at the specified position in the expression.
Warning
This method is meant for performance, for expressions with a dynamic number of dimensions (i.e. not known at compile time). Since it may have undefined behavior (see parameters), operator() should be preferred whenever it is possible.
Warning
This method is NOT compatible with broadcasting, meaning the following code has undefined behavior:
xt::xarray<double> a = {{0, 1}, {2, 3}}; xt::xarray<double> b = {0, 1}; auto fd = a + b; double res = fd.unchecked(0, 1);
- Parameters
args – a list of indices specifying the position in the expression. Indices must be unsigned integers, the number of indices must be equal to the number of dimensions of the expression, else the behavior is undefined.
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template<class It>
inline auto element(It first, It last) const -> const_reference¶ Returns a constant reference to the element at the specified position in the function.
- Parameters
first – iterator starting the sequence of indices
last – iterator ending the sequence of indices The number of indices in the sequence should be equal to or greater than the number of dimensions of the container.
Broadcasting
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template<class S>
inline bool broadcast_shape(S &shape, bool reuse_cache = false) const¶ Broadcast the shape of the function to the specified parameter.
- Parameters
shape – the result shape
reuse_cache – boolean for reusing a previously computed shape
- Returns
a boolean indicating whether the broadcasting is trivial
Defined in xtensor/xmath.hpp
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template<class F, class ...E>
inline auto xt::make_lambda_xfunction(F &&lambda, E&&... args)¶ Create a xfunction from a lambda.
This function can be used to easily create performant xfunctions from lambdas:
template <class E1> inline auto square(E1&& e1) noexcept { auto fnct = [](auto x) -> decltype(x * x) { return x * x; }; return make_lambda_xfunction(std::move(fnct), std::forward<E1>(e1)); }
Lambda function allow the reusal of a single arguments in multiple places (otherwise only correctly possible when using xshared_expressions).
auto
lambda functions are automatically vectorized withxsimd
if possible (note that the trailing-> decltype(...)
is mandatory for the feature detection to work).- Parameters
lambda – the lambda to be vectorized
args – forwarded arguments
- Returns
lazy xfunction