Description of compressed1D

compressed1D<T, SizeType = int, int IND_OFFSET = index_from_zero>		Programmers Guide
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Component type:type

Description

The compressed1D Vector is a sparse vector implemented with a pair of parallel arrays. One array is for the element values, and the other array is for the indices of those elements. The elements are ordered by their index as they are inserted into the compressed1D. compressed1D's can be used to build matrices with the array storage format, and they can also be used on their own.

 [ (1.2, 3), (4.6, 5), (1.0, 10), (3.7, 32) ] A Sparse Vector

 [ 1.2, 4.6, 1.0, 3.7 ]  Value Array
 [  3,   5,  10,  32 ]   Index Array

The compressed1D::iterator dereferences (*i) to return the element value. One can access the index of that element with the i.index() function. One can also access the array of indices through the nz_struct() method.

One particularly useful fact is that one can perform scatters and gathers of sparse elements by using the mtl::copy(x,y) function with a sparse and a dense vector. This method does not change the size() of the vector.

Example

In gather_scatter.cc:

void do_gather_scatter(DenseVec& d, SparseVec& c) {
  using namespace mtl;

  c[2] = 0;
  c[5] = 0;
  c[7] = 0;

  gather(d,c);
  scale(c,2.0);
  scatter(c,d);
  typedef dense1D<double> denseVec;
  typedef compressed1D<double> compVec;
  denseVec d(9,2);
  compVec c;
  do_gather_scatter(d, c);

More examples can be found in array2D.cc, sparse_copy.cc

Definition

compressed1D.h

Template Parameters

Parameter	Description	Default
`T`	the element type
`SizeType`	the type for the stored indices	`int`
`IND_OFFSET`	To handle indexing from 0 or 1	`index_from_zero`

Model of

Vector

Members

Member	Where defined	Description
`enum { N = 0 }`
`sparsity`		This is a sparse vector
`dimension`		This is a 1D container
`scaled_type`		Scaled type of this vector
`value_type`		Element type
`pointer`		A pointer to the element type
`size_type`		Unsigned integral type for dimensions and indices
`difference_type`		Integral type for differences in iterators
`reference`		Reference to the value type
`const_reference`		Const reference to the value type
`iterator`		Iterator type
`const_iterator`		Const iterator type
`reverse_iterator`		Reverse iterator type
`const_reverse_iterator`		The const reverse iterator type
`IndexArrayRef`		Reference to the index array
`IndexArray`		The type for the index array
`subrange_type`		The type for the subrange vector
`compressed1D ()`		Default Constructor
`compressed1D (size_type n)`		Length N Constructor
`compressed1D (const self& x)`		Copy Constructor
`template <class IndexIter> compressed1D (IndexIter first, IndexIter last, size_type n)`		Index Array Constructor
`self& operator= (const self& x)`		Assignment Operator
`iterator begin ()`	Container	Return an iterator pointing to the beginning of the vector
`iterator end ()`	Container	Return an iterator pointing past the end of the vector
`const_iterator begin () const`	Container	Return a const iterator pointing to the begining of the vector
`const_iterator end () const`	Container	Return a const iterator pointing past the end of the vector
`reverse_iterator rbegin ()`	Reversible Container	Return a reverse iterator pointing to the last element of the vector
`reverse_iterator rend ()`	Reversible Container	Return a reverse iterator pointing past the end of the vector
`const_reverse_iterator rbegin () const`	Reversible Container	Return a const reverse iterator pointing to the last element of the vector
`const_reverse_iterator rend () const`	Reversible Container	Return a const reverse iterator pointing past the end of the vector
`reference operator[] (size_type i)`		Access the element with index i
`const_reference operator[] (size_type i) const`		Access the element with index i
`iterator insert (size_type i, const T& val)`		Insert val into the vector at index i
`void push_back (size_type i, const T& val)`		Push back, warning: must insert elements ordered by index.
`void clear ()`		Erase the vector
`size_type size () const`		The size of the vector (including non-zeroes)
`size_type nnz () const`		The number of non-zero elements (the number stored)
`void resize (size_type n)`		Resize the vector to size n
`void reserve (size_type n)`		Reserve storage for n non-zero elements
`IndexArrayRef nz_struct () const`		Returns the array of indices
`IndexArrayRef nz_struct ()`		Returns the array of indices

New members

Notes

See also