Initial commit

Eigen3/doc/snippets/MatrixBase_array_const.cpp

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+Vector3d v(-1,2,-3);
+cout << "the absolute values:" << endl << v.array().abs() << endl;
+cout << "the absolute values plus one:" << endl << v.array().abs()+1 << endl;
+cout << "sum of the squares: " << v.array().square().sum() << endl;