Vectors are instances of the class Vector
. Class Vector
is a template class: Vector<T, Storage, Allocator>
. T
is the type of the elements to be stored (e.g. double
). Storage
defines how the vector is stored. Storage
is equal to VectFull
by default for full vectors, you can set it to VectSparse
for sparse vectors. Finally, Allocator
defines the way memory is managed. It is close to STL allocators. See the section "Allocators" for further details.
There is a default Allocator
(see the section "Allocators") and a default Storage
(VectFull
). It means that these two template parameters may be omitted. Then a vector of integers may be declared thanks to the line:
Vector<int> V;
This defines a vector of size 0, that is to say an empty vector. To define a vector of length 5, one may write:
Vector<int> V(5);
Other declarations may be:
Vector<int, VectFull> V(10); Vector<int> U(V); // Copy constructor. Vector<int, VectFull, MallocAlloc<int> > V(10); Vector<int, VectFull, NewAlloc<int> > V(10);
Access to elements is achieved through the operator(int)
, and indices start at 0:
Vector<int, VectFull> V(10); V(5) = -3; V(0) = 2 * V(5);
To display vectors, there are two convenient options:
V.Print(); std::cout << V << std::endl;
There are lots of methods that are described in the documentation. One may point out:
Fill
fills with 0, 1, 2, 3, etc. or fills the vector with a given value.
GetLength
or GetSize
return the length of the vector.
Reallocate
resizes the vector (warning, data may be lost, depending on the allocator).
Resize
resizes the vector while keeping previous entries.
PushBack
inserts an element at the end of the vector.
Read
, ReadText
, Write
, WriteText
are useful methods for input/ouput operations.
A comprehensive test of dense vectors is achieved in file test/program/vector_test.cpp
.
There is a default Allocator
(see the section "Allocators"). It means that this template parameter may be omitted. Then a sparse vector of doubles may be declared thanks to the line:
Vector<double, VectSparse> V;
This defines a null vector, that is to say that V(i)
will return 0 for all i. To define a vector with 5 non-zero entries, one may write:
Vector<double, VectSparse> V(5);
Other declarations may be:
Vector<double, VectSparse> U(V); // Copy constructor. Vector<int, VectSparse, MallocAlloc<int> > V(10); Vector<int, VectSparse, NewAlloc<int> > V(10);
A good technique consists of modifying those vectors through methods AddInteraction
and AddInteractionRow
. These methods insert (or add) the elements at the correct position, so that the row numbers are always sorted in ascending order. You can use them as in the following example :
Vector<double, VectSparse> V; cout << "Empty vector V = " << V << endl; // non-null value of 1.5 at row 2 V.AddInteraction(2, 1.5); V.AddInteraction(2, 0.8); // now V(2) should be equal to 1.5+0.8 = 2.3 cout << "After AddInteraction, V = " << V << endl; // AddInteractionRow for several rows to add IVect num(2); Vector<double> val(2); num(0) = 1; val(0) = -0.4; num(1) = 4; val(1) = 0.6; V.AddInteractionRow(num, val); cout << "After AddInteractionRow, V = " << endl << V << endl;
The output of this code would read :
Empty vector V = After AddInteraction, V = 3 2.3 AfterAddInteractionRow, V = 2 -0.4 3 2.3 5 0.6
You noticed that the row indices are displayed with indices beginning at 1 instead of 0, this is more convenient for debugging, or exporting datas into Matlab for example.
You can also use the operator(int)
to modify directly values.
Vector<double, VectSparse> V; V(5) = -3; V(0) = 2 * V(5);
If the non-zero entry doesn't exist, it is created at the correction position as for AddInteraction
.
The methods Reallocate
, Index
and Value
can also be used, but they need to be used carefully and often the method Assemble
has to be called in order to sort non-zero entries.
// 3 non-zero entries Vector<double, VectSparse> V; // creation of 3 non-zero entries V.Reallocate(3); // initialization of non-zero entries with Index and Value V.Index(0) = 1; // row number of first entry V.Value(0) = 1.3; // value of first entry V.Index(1) = 3; V.Value(1) = -0.5; V.Index(2) = 2; V.Value(2) = 2.7; // Here the row numbers are not sorted // you need to call Assemble V.Assemble();
In the same way, the method SetData
can be used in conjunction with Assemble
:
Vector<double, VectSparse> V; IVect row(3); Vector<double> value(3); row(0) = 1; // row number of first entry value(0) = 1.3; // value of first entry row(1) = 3; value(1) = -0.5; row(2) = 2; value(2) = 2.7; // feeding V with row and value V.SetData(value, row); // Here the row numbers are not sorted // you need to call Assemble V.Assemble();
You may notice that the method SetData empties vectors row and value.
There are lots of methods that are described in the documentation. One may point out:
Fill
give to non-zero entries the value 0, 1, 2, 3, etc. or a given value.
GetLength
or GetSize
return the number of non-zero entries.
Read
, ReadText
, Write
, WriteText
are useful methods for input/ouput operations.
A comprehensive test of dense vector is achieved in file test/program/sparse_vector_test.cpp
.