Initial commit

external/eigen-3.4.0/doc/snippets/TopicAliasing_mult2.cpp

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+MatrixXf matA(2,2), matB(2,2); 
+matA << 2, 0,  0, 2;
+
+// Simple but not quite as efficient
+matB = matA * matA;
+cout << matB << endl << endl;
+
+// More complicated but also more efficient
+matB.noalias() = matA * matA;
+cout << matB;