Eigenvalues and eigenfunctions 44 Eigen-value 8 Principal component analysis 6 Covariance matrix 5 Quantum theory 5 eigenvalues 5 Covariance matrices 4 Eigenvalue and eigenfunctions 4 Damping 3 Damping torque coefficients 3 Eigenvalue problem 3 Eigenvalues 3 Electric power transmission 3 Hamiltonians 3 Machine learning 3 Optimisations 3 Particle swarm optimization (PSO) 3 Principal-component analysis 3 Spectrum analysis 3 article 3 Angle stability 2 Asymptotic stability 2 Budget control 2 China 2 Computer programming 2 Controllers 2 Convergence 2 Covariance matrix estimation 2 Crystal symmetry 2 Decision trees 2