- Commit
- 5e7748a21a23832587a34c8ecba5d48e990f9f39
- Parent
- b38ce71bf13d0c6f315b8310a0f60733eb7525cb
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Fixed some typos and removed unecessary whitespace
Riemannian Geometry course project on the manifold H¹(I, M) of class H¹ curves on a Riemannian manifold M and its applications to the geodesics problem
Fixed some typos and removed unecessary whitespace
2 files changed, 29 insertions, 29 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/introduction.tex | 2 | 1 | 1 |
Modified | sections/structure.tex | 56 | 28 | 28 |
diff --git a/sections/introduction.tex b/sections/introduction.tex @@ -67,7 +67,7 @@ bundles. % TODO: Finilize this We should point out that due to limitations of space we will primarily focus on -the broad strokes of the theory ahead. Many results are left unprovred, but we +the broad strokes of the theory ahead. Many results are left unproved, but we will include references to other materials containing proofs. We'll assume basic knowledge of differential and Riemannian geometry, as well as some familiarity with the classical theory of the calculus of variations -- see
diff --git a/sections/structure.tex b/sections/structure.tex @@ -11,7 +11,7 @@ Given an interval \(I\), recall that a continuous curve \(\gamma : I \to continuous, \(\dot \gamma(t)\) exists for almost all \(t \in I\) and \(\dot\gamma \in L^2(I, \RR^n)\). It is a well known fact that the so called \emph{Sobolev space \(H^1(I, \RR^n)\)} of all class \(H^1\) curves in \(\RR^n\) -is a Hilbert space under the inner product given by +is a Hilbert space under the inner product given by \[ \langle \gamma, \eta \rangle_1 = \int_0^1 \gamma(t) \cdot \eta(t) + \dot\gamma(t) \cdot \dot\eta(t) \; \dt @@ -68,11 +68,11 @@ approach \(\ell(\gamma) = \sqrt 2\) as \(n\) approaches \(\infty\). \centering \begin{tikzpicture} \draw (4, 1) -- (1, 4); - \draw (4, 1) -- (4, 2) - -- (3, 2) - -- (3, 3) node[right]{$\gamma_n$} - -- (2, 3) node[left]{$\gamma$} - -- (2, 4) + \draw (4, 1) -- (4, 2) + -- (3, 2) + -- (3, 3) node[right]{$\gamma_n$} + -- (2, 3) node[left]{$\gamma$} + -- (2, 4) -- (1, 4); \draw[dotted] (4.5, .5) -- (4, 1); \draw[dotted] (.5, 4.5) -- (1, 4); @@ -90,7 +90,7 @@ The issue with this particular example is that while \(\gamma_n \to \gamma\) uniformly, \(\dot\gamma_n\) does not converge to \(\dot\gamma\) in the uniform topology. This hints at the fact that in order to \(E\) and \(\ell\) to be continuous maps we need to control both \(\gamma\) and \(\dot\gamma\). Hence a -natural candidate for a norm in \({C'}^\infty(I, \RR^n)\) is +natural candidate for a norm in \({C'}^\infty(I, \RR^n)\) is \[ \norm{\gamma}_1^2 = \norm{\gamma}_0^2 + \norm{\dot\gamma}_0^2, \] @@ -104,7 +104,7 @@ it is natural to expect \({C'}^\infty(I, \RR^n)\) to be Banach space. In particular, \({C'}^\infty(I, \RR^n)\) must be a normed Banach space. This is unfortunately not the case for \({C'}^\infty(I, \RR^n)\) the norm \(\norm\cdot_1\), but we can consider its completion, which, by a classical -result by Lebesgue, just so happens to coincide with \(H^1(I, M)\). +result by Lebesgue, just so happens to coincide with \(H^1(I, M)\). It's also interesting to note that the completion of \({C'}^\infty(I, \RR^n)\) with respect to the norm \(\norm\cdot_\infty\) is the space \(C^0(I, \RR^n)\) @@ -126,7 +126,7 @@ find\dots of \(E\) is the completion of the space \({C'}^\infty(E)\) of peace-wise smooth sections of \(E\) under the inner product given by \[ - \langle \xi, \eta \rangle_1 + \langle \xi, \eta \rangle_1 = \int_0^1 \langle \xi_t, \eta_t \rangle + \langle \nabla \xi_t, \nabla \eta_t \rangle \; \dt \] @@ -166,13 +166,13 @@ find\dots \[ \begin{split} \norm{\xi}_\infty^2 - & = \norm{\xi_{t_0}}^2 + & = \norm{\xi_{t_0}}^2 + \int_{t_0}^{t_1} \frac{\dd}{\dd s} \norm{\xi_s}^2 \; \dd s \\ \text{(\(\nabla\) is compatible with the metric)} - & = \norm{\xi_{t_0}}^2 + & = \norm{\xi_{t_0}}^2 + 2 \int_{t_0}^{t_1} \langle \xi_s, \nabla \xi_s \rangle \; \dd s \\ \text{(Cauchy-Schwarz)} - & \le \norm{\xi_{t_0}}^2 + & \le \norm{\xi_{t_0}}^2 + 2 \int_0^1 \norm{\xi_s} \cdot \norm{\nabla \xi_s} \; \dd s \\ & \le \norm{\xi}_0^2 + \norm{\xi}_0^2 + \norm{\nabla \xi}_0^2 \\ & \le 2 \norm{\xi}_1^2 @@ -222,7 +222,7 @@ We begin with a technical lemma. Let \(C^0(W_\gamma) = \{ X \in C^0(\gamma^* TM) : X_t \in W_{\gamma, t} \; \forall t \}\). We claim \(C^0(W_\gamma)\) is open in \(C^0(\gamma^* TM)\). Indeed, given \(X \in C^0(W_\gamma)\) there exists \(\delta > 0\) such - that + that \[ \begin{split} \norm{X - Y}_\infty < \delta @@ -240,7 +240,7 @@ We begin with a technical lemma. Let \(W \subset TM\) be an open neighborhood of the zero section in \(TM\) such that \(\exp\!\restriction_W : W \to \exp(W)\) is invertible -- whose existence follows from the fact that the injectivity radius depends continuously on \(p -\in M\). +\in M\). \begin{definition} Given \(\gamma \in {C'}^\infty(I, M)\) let \(W_\gamma, W_{\gamma, t} \subset @@ -249,7 +249,7 @@ follows from the fact that the injectivity radius depends continuously on \(p \arraycolsep=1pt \begin{array}{rl} \exp_\gamma : H^1(W_\gamma) & \to H^1(I, M) \\ - X & + X & \begin{array}[t]{rl} \mapsto \exp \circ X : I & \to M \\ t & \mapsto \exp_{\gamma(t)}(X_t) @@ -278,7 +278,7 @@ M)\). Moreover, since \({C'}^\infty(I, M)\) is dense, \(\{U_\gamma\}_{\gamma \in {C'}^\infty(I, M)}\) is an open cover of \(H^1(I, M)\). The real difficulty of this proof is showing that the transition maps \[ - \exp_\eta^{-1} \circ \exp_\gamma : + \exp_\eta^{-1} \circ \exp_\gamma : \exp_\gamma^{-1}(U_\gamma \cap U_\eta) \subset H^1(\gamma^* TM) \to H^1(\eta^* TM) \] @@ -287,9 +287,9 @@ leave this details we leave as an exercise to the reader -- see theorem 2.3.12 of \cite{klingenberg} for a full proof. The charts \(\exp_\gamma^{-1}\) are modeled after separable Hilbert spaces, -with tipical representatives \(H^1(\gamma^* TM) \cong H^1(I, +with typical representatives \(H^1(\gamma^* TM) \cong H^1(I, \RR^n)\)\footnote{Any trivialization of $\gamma^* TM$ induces an isomorphism -$H^1(\gamma^* TM) \isoto H^1(I, \RR^n)$.}. +$H^1(\gamma^* TM) \isoto H^1(I, \RR^n)$.}. It's interesting to note that this construction is functorial. More precisely\dots @@ -307,14 +307,14 @@ precisely\dots We would also like to point out that this is a particular case of a more general construction: that of the Banach manifold \(H^1(E)\) of class \(H^1\) -sections of a smooth fiber bundle \(E \to I\) -- not necessarity a vector +sections of a smooth fiber bundle \(E \to I\) -- not necessarily a vector bundle. Our construction of \(H^1(I, M)\) is equivalent to of of the manifold \(H^1(I \times M)\) in the sense that the canonical map \[ \arraycolsep=1pt \begin{array}{rl} \tilde{\cdot} : H^1(I, M) \to & H^1(I \times M) \\ - \gamma \mapsto & + \gamma \mapsto & \begin{array}[t]{rl} \tilde\gamma : I & \to I \times M \\ t & \mapsto (t, \gamma(t)) @@ -328,7 +328,7 @@ The space \(H^1(E)\) is modeled after the Hilbert spaces \(H^1(F)\) of class of a vector bundle -- the so called \emph{vector bundle neighborhoods of \(E\)}. This construction is highlighted in great detail and generality in the first section of \cite[ch.~11]{palais}, but unfortunately we cannot afford such -a divergion in this short notes. Having saied that, we are now finally ready to +a diversion in this short notes. Having said that, we are now finally ready to discuss the Riemannian structure of \(H^1(I, M)\). \subsection{The Metric of \(H^1(I, M)\)} @@ -337,8 +337,8 @@ We begin our discussion of the Riemannian structure of \(H^1(I, M)\) by looking at its tangent bundle. Notice that for each \(\gamma \in {C'}^\infty(I, M)\) the chart \(\exp_\gamma^{-1} : U_\gamma \to H^1(\gamma^* TM)\) induces a canonical isomorphism \(\phi_\gamma : T_\gamma H^1(I, M) \isoto H^1(\gamma^* -TM)\), as described in propostion~\ref{thm:tanget-space-topology}. In fact, -this isomorphisms may be extended to a cononical isomorphism of vector bundles, +TM)\), as described in proposition~\ref{thm:tanget-space-topology}. In fact, +this isomorphisms may be extended to a canonical isomorphism of vector bundles, as seen in\dots \begin{lemma} @@ -348,7 +348,7 @@ as seen in\dots \[ \arraycolsep=1pt \begin{array}{rl} - \psi_{i, \gamma} : H^1(U_\gamma) \times H^i(\gamma^* TM) \to + \psi_{i, \gamma} : H^1(U_\gamma) \times H^i(\gamma^* TM) \to & \prod_{\eta \in H^1(I, M)} H^i(\eta^* TM) \\ (X, Y) \mapsto & \begin{array}[t]{rl} @@ -372,12 +372,12 @@ as seen in\dots \begin{proof} Note that the sets \(H^1(U_\gamma) \times T_\gamma H^1(I, M)\) are precisely - the images of the canonical charts + the images of the canonical charts \[ - \varphi_\gamma : + \varphi_\gamma : \varphi_\gamma^{-1}(H^1(U_\gamma) \times T_\gamma H^1(I, M)) \subset T H^1(I, M) - \to H^1(U_\gamma) \times T_\gamma H^1(I, M) + \to H^1(U_\gamma) \times T_\gamma H^1(I, M) \] of \(T H^1(I, M)\). @@ -392,7 +392,7 @@ as seen in\dots {C'}^\infty(I, M)\) is given by \(\phi_\gamma\). \end{proof} -This las result will be the basis for our analysis of the Riemannian structure +This last result will be the basis for our analysis of the Riemannian structure of \(H^1(I, M)\). We may now describe the metric of \(H^1(I, M)\) in terms of the fibers \(T_\gamma H^1(I, M) \cong H^1(\gamma^* TM)\).