C++ In a Nutshell

Name

gslice class — Generalized slice

Synopsis

class gslice {
public:
  gslice(  );
  gslice(size_t start, const valarray<size_t>& size, 
         const valarray<size_t>& stride);
  size_t start(  ) const;
  valarray<size_t> size(  ) const;
  valarray<size_t> stride(  ) const;
};

The gslice class describes a generalized slice of a valarray. A generalized slice is a subset of the elements of a valarray, characterized by a starting index and a set of sizes and strides. The size and stride arrays must have the same size. Each size/stride pair denotes a set of elements at periodic indices. The number of elements in the generalized slice is equal to the product of the values in the size array. The elements are taken from a valarray at each index i:

i = start + Σ k j × stride j

in which kj takes all the values in the range [0, size[j]), and j is in the range [0, stride.size( )). The highest value of j varies fastest. With a single element in stride and size, gslice is the same as plain slice. Example 13-41 demonstrates gslice more clearly. Pay particular attention to the final gslice, where you can see how the indices advance, first with a stride of 3 (k1 ranges from 0 to 2), then with a stride of 2 (k0 ranges from 0 to 3)

Example

Example 13-41. Generalized slicing of a valarray

// Construct valarray objects from a few integers. std::valarray<std::size_t> va(std::size_t a0) { std::valarray<std::size_t> result(1); result[0] = a0; return result; } std::valarray<std::size_t> va(std::size_t a0, std::size_t a1) { std::valarray<std::size_t> ...