initial commit

third_party/eigen/doc/snippets/Triangular_solve.cpp

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+Matrix3d m = Matrix3d::Zero();
+m.triangularView<Eigen::Upper>().setOnes();
+cout << "Here is the matrix m:\n" << m << endl;
+Matrix3d n = Matrix3d::Ones();
+n.triangularView<Eigen::Lower>() *= 2;
+cout << "Here is the matrix n:\n" << n << endl;
+cout << "And now here is m.inverse()*n, taking advantage of the fact that"
+        " m is upper-triangular:\n"
+     << m.triangularView<Eigen::Upper>().solve(n) << endl;
+cout << "And this is n*m.inverse():\n" << m.triangularView<Eigen::Upper>().solve<Eigen::OnTheRight>(n);