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Many problems in the sciences and engineering can be rephrased as optimization problems on matrix search spaces endowed with a so-called manifold structure. This book shows how to exploit the special structure of such problems to develop efficient numerical algorithms. It places careful emphasis on both the numerical formulation of the algorithm and its differential geometric abstraction--illustrating how good algorithms draw equally from the insights of differential geometry, optimization, and numerical analysis. Two more theoretical chapters provide readers with the background in differential geometry necessary to algorithmic development. In the other chapters, several well-known optimization methods such as steepest descent and conjugate gradients are generalized to abstract manifolds. The book provides a generic development of each of these methods, building upon the material of the geometric chapters. It then guides readers through the calculations that turn these geometrically formulated methods into concrete numerical algorithms. The state-of-the-art algorithms given as examples are competitive with the best existing algorithms for a selection of eigenspace problems in numerical linear algebra.

This book provides the first-ever systematic introduction to the theory of Riemannian submersions, which was initiated by Barrett O'Neill and Alfred Gray less than four decades ago. The authors focus their attention on classification theorems when the total space and the fibres have nice geometric properties. Particular emphasis is placed on the interrelation with almost Hermitian, almost contact and quaternionic geometry. Examples clarifying and motivating the theory are included in every chapter. Recent results on semi-Riemannian submersions are also explained. Finally, the authors point out the close connection of the subject with some areas of physics.

As a generalization of anti-invariant submersions, semi-invariant submersions and slant submersions, we introduce the notion of hemi-slant submersion and study such submersions from Kählerian manifolds onto Riemannian manifolds. After we study the geometry of leaves of distributions which are involved in the definition of the submersion, we obtain new conditions for such submersions to be harmonic and totally geodesic. Moreover, we give a characterization theorem for the proper hemi-slant submersions with totally umbilical fibers.

We study Lagrangian submersions whose total manifolds are locally conformal Kähler manifolds. We first investigate the necessary and sufficient conditions for the horizontal and vertical distributions of a Lagrangian submersion from a locally conformal Kähler manifold to be totally geodesic. Then, we examine the harmonicity of these submersions. We prove that the Lee vector field of the total manifold of such a submersion cannot be vertical. In the case of the Lee vector field is horizontal, we show that the horizontal distribution is always integrable and totally geodesic while its fibers cannot be totally geodesic. We obtain fundamental equations for a curve on the total manifold of such submersions to be geodesic. Consequently, we give a necessary and sufficient condition for a Lagrangian submersion to be Clairaut. Finally, we prove that if a Lagrangian submersion from a locally conformal Kähler manifold is a Clairaut submersion, then either its mean curvature vector field is proportional to the horizontal part of its Lee vector field or the vertical distribution of the submersion is one dimensional.

The aim of this paper is to introduce Clairaut conformal submersions between Riemannian manifolds. First, we find necessary and sufficient conditions for conformal submersions to be Clairaut conformal submersions. In particular, we obtain Clairaut relation for geodesics on the total manifolds of conformal submersions, and prove that Clairaut conformal submersions have constant dilation along their fibers, which are totally umbilical, with mean curvature being gradient of a function. Further, we calculate the scalar and Ricci curvatures of the vertical distributions of the total manifolds. Moreover, we find a necessary and sufficient condition for Clairaut conformal submersions to be harmonic. For a Clairaut conformal submersion we find conformal changes of the metric on its domain or image, that give a Clairaut Riemannian submersion, a Clairaut conformal submersion with totally geodesic fibers, or a harmonic Clairaut submersion. Finally, we give two non-trivial examples of Clairaut conformal submersions to illustrate the theory and present a local model of every Clairaut conformal submersion with integrable horizontal distribution.

In this paper, we study conformal submersions from Ricci solitons to Riemannian manifolds with non-trivial examples. First, we study some properties of the O’Neill tensor A in the case of conformal submersion. We also find a necessary and sufficient condition for conformal submersion to be totally geodesic and calculate the Ricci tensor for the total manifold of such a map with different assumptions. Further, we consider a conformal submersion F : M → N from a Ricci soliton to a Riemannian manifold and obtain necessary conditions for the fibers of F and the base manifold N to be Ricci soliton, almost Ricci soliton and Einstein. Moreover, we find necessary conditions for a vector field and its horizontal lift to be conformal on N and ( Ker F ∗ ) ⊥ , respectively. Also, we calculate the scalar curvature of Ricci soliton M . Finally, we obtain a necessary and sufficient condition for F to be harmonic.

Our purpose in this article is to study anti-invariant statistical submersions from holomorphic statistical manifolds. Firstly we introduce holomorphic statistical submersions satisfying the certain condition, after we give anti-invariant statistical submersions satisfying the certain condition. And we supported our results with examples.

In this paper, we describe anti-invariant and Clairaut anti-invariant pseudo-Riemannian submersions (AIPR and CAIPR submersions, respectively, briefly) from para-Kenmotsu manifolds onto Riemannian manifolds. We introduce new Clairaut circumstances for anti-invariant submersions whose total space is para-Kenmotsu manifold. Also, we offer a obvious example of CAIPR submersion.

As a generalization of hemi-slant submersions and semi-slant submersions, we introduce the notion of quasi-bi-slant submersions from almost Hermitian manifolds onto Riemannian manifolds giving some examples and study such submersions from Kähler manifolds onto Riemannian manifolds. We study the geometry of leaves of distributions which are involved in the definition of the submersion. We also obtain conditions for such submersions to be integrable and totally geodesic. Moreover, we give a characterization theorem for proper quasi-bi-slant submersions with totally umbilical fibers.

In the present paper, we introduce a new kind of Riemannian submersion such that the fibers of such submersion are generic submanifolds in the sense of Ronsse that we call generic submersion. Some examples are given for generic submersion. Necessary and sufficient conditions are found for the integrability and totally geodesicness of the distributions which are mentioned in the definition. The geometry of the fibers is investigated. New results are obtained by considering the parallelism condition of canonical structures.