Contents Chapter 1 Basic on Sturm-Liouville Problems 1 1.1 Classes of Sturm-Liouville Problems 1 1.2 Characteristic Function 9 1.3 Equations with Piece-Wise Constant Coeffcients 14 1.4 Sturm's Comparison Theorem and Prufer Transformation 19 Chapter 2 Di.erentiable Manifolds and Lie Groups 31 2.1 Differentiable Manifolds 31 2.2 Differentiable Maps and Tangent Vectors 41 2.3 Complex Manifolds 45 2.4 Lie Groups 48 Chapter 3 Geometric Structures on Spaces of Boundary Conditions 51 3.1 Spaces of Boundary Conditions 52 3.2 Characteristic Curve and Surfaces 59 3.3 Di.erentiability of Continuous Eigenvalue Branches 71 3.4 Analyticity of Continuous Eigenvalue Branches 78 Chapter 4 Inequalities among Eigenvalues 84 4.1 More on Characteristic Function 85 4.2 Asymptotic Analysis of Fundamental Matrix 93 4.3 Inequalities among Eigenvalues for any coupled self-adjoint Boundary Condition 96 4.4 Ranges of on BR and BC 102 4.5 The Relationship among Three Multiplicities of a Di.erential Operator's Eigenvalue 104 Chapter 5 Dependence of the n-th Eigenvalue on the Sturm-Liouville Problem 118 5.1 Continuity Principle 120 5.2 Continuous Dependence of on the Differential Equation 120 5.3 Discontinuity of λn 122 5.4 Comments on Di.erentiability of λn 131 5.5 The Index Problem for Eigenvalues for Coupled Boundary Conditions 135 Appendix A Fist-Order Linear Di.erential Equations 150 A.1 Existence and Uniqueness of Solution 150 A.2 Rank of a Solution and Variation of Parameters 155 A.3 Continuous Dependence of Solution on Problem 158 References 161 Index 170