16. Slicing

In this section, IM denotes some IndexMaps.

• We refer here to any partial view of the arrays as “slicing”, i.e. subarrays, true slices, etc… A slicing is any (meta)-function that take an indexmap and return another one.

• It is a meta-function that computes the type of the resulting indexmap
• It is a function that computes the resulting indexmap.

• The array/matrix/vector classes and their views, when called with the () operator, will:

• forward all the arguments and their types to IndexMaps::slice, to compute the new indexmap IM2.
• If IM2 is of dimension 0, return a value_type & or const & (it is a simple number, not an array).
• Otherwise: return a new view, made of IM2 and the same data as for the original object.

• Possible slices are defined by the IndexMap type. Slicing an class C with IndexMap I1 produces a class C2_view, with IndexMap I2, i.e. a new sliced IndexMap on the same data.
• Examples:

• array and array_view can be sliced:

``

array<T,2> A(10,10); : defines an array A(1,2) : element access. A ( 1, range(0,2) ) : 1d slice A( range(0,10,2), range(0,10,2)) : a 2d slice viewing every each elements with even coordinates.

``

• matrix, matrix_view when sliced, return vector_view or matrix_view.

• One can be much more general: e.g. slicing the diagonal of a matrix, etc…
• Implementation is entirely done in the IndexMaps classes, by specializing 2 templates

(basically by writing the function IM1-> IM2). The rest is done by indexmap_storage_pair class, which will compute the correct view class depending on the view class and IM2 (view_from_tag_I_S template).

::

//In namespace IndexMaps::result_of template<typename IM, typename ArgsTuple> struct slice< IM, ArgsTuple> { typedef IM2 type; };

//In namespace IndexMaps: template<typename IM, typename ArgsTuple> typename result_of::slice<IM,ArgsTuple>::type slice(IM const &, ArgsTuple args);