sub-vectors and sub-matrices

It is possible to obtain any sub-vector or sub-matrix of a fully interfaced object. There are four types of sub indexes.

gmm::sub_interval(first, length);

represents an interval whose first index is first and length is length ( for instance gmm::sub_interval(10, 3); represents the indexes {10, 11, 12} ).  

gmm::sub_slice(first, length, step);

represents also an interval in which one index over step is taken. ( for instance gmm::sub_slice(10, 3, 2); represents the indexes {10, 12, 14} )

gmm::sub_index(CONT c);

represents the sub-index which is the collection of index contained in the container c. For instance  

std::vector<size_t> c(3);
c[0] = 1; c[1] = 3; c[2] = 16;
gmm::sub_index(c);

represents the indexes {1, 3, 16} .
VERY IMPORTANT : the container c has to be sorted from the smaller index to the greater one (i.e. with increasing order) and no repetition is allowed.
For unsorted index such as permutation, a special type of sub index is defined:
 

gmm::unsorted_sub_index(CONT c);

Some algorithms are a little bit slower with unsorted sub indexes.

 

Now gmm::sub_vector(V, subi) gives a reference to a sub-vector:

gmm::vsvector<double> V(10);
V[5] = 3.0;
std::cout << gmm::sub_vector(V, gmm::sub_interval(2, 3)) << std::endl;

prints to the standard output V[2], V[3] and V[4].
  gmm::sub_matrix(V, subi1, subi2) gives a reference to a sub-matrix. For instance:

gmm::col_matrix< gmm::wsvector<double> > M(5, 20);
M(3, 2) = 5.0;
std::cout << gmm::sub_matrix(M, gmm::sub_interval(2, 3), gmm::sub_interval(2, 3))
          << std::endl;

prints to the output a sub-matrix. If the two sub-indexes are equal, it is possible to omit the second. For instance:

gmm::col_matrix< gmm::wsvector<double> > M(5, 20);
M(3, 2) = 5.0;
std::cout << gmm::sub_matrix(V, gmm::sub_interval(2, 3)) << std::endl;

The reference on sub_matrix is writable if the corresponding matrix is writable (so you can copy on a sub_matrix, add sub-matrices ...).

row and column of a matrix

  gmm::mat_row(M, i) gives a (possibly writable) reference to the row i of matrix M, and gmm::mat_col(M, i) gives a (possibly writable) reference to the column i. It is not possible to access to the rows if M is a column matrix and to the columns if it is a row matrix. It is possible to use gmm::mat_const_row(M, i) and gmm::mat_const_col(M, i) to have constant references.