2. Strategy

All the classes are a combination of a system of indices (called IndexMap I in the following) and a physical storage S in the computer (a block of memory), denoted as an IndexMap_Storage_Pair (I,S).

  • I models the IndexMap concept [REF below].

  • It is the bijection between the a set of indices and the position in the memory block. It can be though as a coordinate system on the (linear) memory block.

  • Various types of indices are possible (only the first is implemented now).

    • cuboid (the standard hypercubic array, the only one currently implemented)
    • triangular arrays
    • band matrix
    • multi-indices, with indices made of pair<int,int> e.g.
  • S models the Storage concept [REF].

  • It is a handle to the memory block containing the actual data.

  • It can be e.g.:

    • a C++ shared pointer to a memory block.
    • a documentation/manual/triqs to a numpy array.

This design has several consequences:

  • Interoperability: classes are widely interoperable, e.g. one can add a array and a matrix (if dimensions are ok of course). one can also add a python numpy and a C++ array without any further coding.
  • It is straighforward to construct a matrix_view<T> from an array<T,2>, since it is the same couple <I,S>, just interpreted differently.
  • It is easy to view a array<T,4> as a matrix by gathering indices (properly ordered in memory): one just has to provide a new IndexMap I2 to see the same data. [ –> very useful for vertex computation in many body…]
  • Slicing, or partial view is very natural: it is just a function on indexmaps: I–> I2, independantly of any storage.

3. Quick guide through the implementation

The implementation is divided into basically 4 parts:

  • Storages: implements two storages shared_block and numpy
  • IndexMaps: implements cuboid index map, its domain and iterators
  • impl/indexmap_storage_pair.hpp: the basic implementation class for all user class. It is basically just a couple of an indexmap and a storage, with shallow copy. It also forward the slices to the indexmap and construct the correct views.
  • upper level: * user class: array, array_view, matrix, matrix_view, vector, vector_view * expression.hpp: boost proto expression * numpy_interface.hpp: helper to get numpy into array * lapack/blas interface * hdf5 support.