Difference between revisions of "cpp/numeric/valarray/slice"
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Revision as of 13:38, 2 November 2012
| Defined in header <valarray>
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| class slice; |
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std::slice is the selector class that identifies a subset of std::valarray similar to BLAS slice. An object of type std::slice holds three values: the starting index, the stride, and the total number of values in the subset. Objects of type std::slice can be used as indexes with valarray's operator[].
Member functions
| constructs a slice (public member function) | |
| accesses the start of the slice (public member function) | |
| accesses the size of the slice (public member function) | |
| accesses the stride of the slice (public member function) |
Example
Barebones valarray-backed Matrix class with a trace calculating function.
Run this code
#include <iostream> #include <valarray> class Matrix { std::valarray<int> data; int dim; public: Matrix(int r, int c) : data(r*c), dim(c) {} int& operator()(int r, int c) {return data[r*dim + c];} int trace() const { return data[std::slice(0, dim, dim+1)].sum(); } }; int main() { Matrix m(3,3); int n = 0; for(int r=0; r<3; ++r) for(int c=0; c<3; ++c) m(r, c) = ++n; std::cout << "Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is " << m.trace() << '\n'; }
Output:
Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is 15
