{"id":357875,"date":"2017-01-25T14:23:03","date_gmt":"2017-01-25T22:23:03","guid":{"rendered":"https:\/\/newed.any0.dpdns.org\/en-us\/research\/?post_type=msr-research-item&#038;p=357875"},"modified":"2018-10-16T20:01:47","modified_gmt":"2018-10-17T03:01:47","slug":"reconstruction-trees-exponential-moment-bounds-linear-estimators","status":"publish","type":"msr-research-item","link":"https:\/\/newed.any0.dpdns.org\/en-us\/research\/publication\/reconstruction-trees-exponential-moment-bounds-linear-estimators\/","title":{"rendered":"Reconstruction on Trees: Exponential Moment Bounds for Linear Estimators"},"content":{"rendered":"<p>Consider a Markov chain <span id=\"MathJax-Element-1-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-1\" class=\"math\"><span id=\"MathJax-Span-2\" class=\"mrow\"><span id=\"MathJax-Span-3\" class=\"mo\">(<\/span><span id=\"MathJax-Span-4\" class=\"msubsup\"><span id=\"MathJax-Span-5\" class=\"mi\">\u03be<\/span><span id=\"MathJax-Span-6\" class=\"mi\">v<\/span><\/span><span id=\"MathJax-Span-7\" class=\"msubsup\"><span id=\"MathJax-Span-8\" class=\"mo\">)<\/span><span id=\"MathJax-Span-9\" class=\"texatom\"><span id=\"MathJax-Span-10\" class=\"mrow\"><span id=\"MathJax-Span-11\" class=\"mi\">v<\/span><span id=\"MathJax-Span-12\" class=\"mo\">\u2208<\/span><span id=\"MathJax-Span-13\" class=\"mi\">V<\/span><\/span><\/span><\/span><span id=\"MathJax-Span-14\" class=\"mo\">\u2208<\/span><span id=\"MathJax-Span-15\" class=\"mo\">[<\/span><span id=\"MathJax-Span-16\" class=\"mi\">k<\/span><span id=\"MathJax-Span-17\" class=\"msubsup\"><span id=\"MathJax-Span-18\" class=\"mo\">]<\/span><span id=\"MathJax-Span-19\" class=\"mi\">V<\/span><\/span><\/span><\/span><\/span> on the infinite <span id=\"MathJax-Element-2-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-20\" class=\"math\"><span id=\"MathJax-Span-21\" class=\"mrow\"><span id=\"MathJax-Span-22\" class=\"mi\">b<\/span><\/span><\/span><\/span>-ary tree <span id=\"MathJax-Element-3-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-23\" class=\"math\"><span id=\"MathJax-Span-24\" class=\"mrow\"><span id=\"MathJax-Span-25\" class=\"mi\">T<\/span><span id=\"MathJax-Span-26\" class=\"mo\">=<\/span><span id=\"MathJax-Span-27\" class=\"mo\">(<\/span><span id=\"MathJax-Span-28\" class=\"mi\">V<\/span><span id=\"MathJax-Span-29\" class=\"mo\">,<\/span><span id=\"MathJax-Span-30\" class=\"mi\">E<\/span><span id=\"MathJax-Span-31\" class=\"mo\">)<\/span><\/span><\/span><\/span> with irreducible edge transition matrix <span id=\"MathJax-Element-4-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-32\" class=\"math\"><span id=\"MathJax-Span-33\" class=\"mrow\"><span id=\"MathJax-Span-34\" class=\"mi\">M<\/span><\/span><\/span><\/span>, where <span id=\"MathJax-Element-5-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-35\" class=\"math\"><span id=\"MathJax-Span-36\" class=\"mrow\"><span id=\"MathJax-Span-37\" class=\"mi\">b<\/span><span id=\"MathJax-Span-38\" class=\"mo\">\u2265<\/span><span id=\"MathJax-Span-39\" class=\"mn\">2<\/span><\/span><\/span><\/span>, <span id=\"MathJax-Element-6-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-40\" class=\"math\"><span id=\"MathJax-Span-41\" class=\"mrow\"><span id=\"MathJax-Span-42\" class=\"mi\">k<\/span><span id=\"MathJax-Span-43\" class=\"mo\">\u2265<\/span><span id=\"MathJax-Span-44\" class=\"mn\">2<\/span><\/span><\/span><\/span> and <span id=\"MathJax-Element-7-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-45\" class=\"math\"><span id=\"MathJax-Span-46\" class=\"mrow\"><span id=\"MathJax-Span-47\" class=\"mo\">[<\/span><span id=\"MathJax-Span-48\" class=\"mi\">k<\/span><span id=\"MathJax-Span-49\" class=\"mo\">]<\/span><span id=\"MathJax-Span-50\" class=\"mo\">=<\/span><span id=\"MathJax-Span-51\" class=\"mo\">{<\/span><span id=\"MathJax-Span-52\" class=\"mn\">1<\/span><span id=\"MathJax-Span-53\" class=\"mo\">,<\/span><span id=\"MathJax-Span-54\" class=\"mo\">.<\/span><span id=\"MathJax-Span-55\" class=\"mo\">.<\/span><span id=\"MathJax-Span-56\" class=\"mo\">.<\/span><span id=\"MathJax-Span-57\" class=\"mo\">,<\/span><span id=\"MathJax-Span-58\" class=\"mi\">k<\/span><span id=\"MathJax-Span-59\" class=\"mo\">}<\/span><\/span><\/span><\/span>. We denote by <span id=\"MathJax-Element-8-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-60\" class=\"math\"><span id=\"MathJax-Span-61\" class=\"mrow\"><span id=\"MathJax-Span-62\" class=\"msubsup\"><span id=\"MathJax-Span-63\" class=\"mi\">L<\/span><span id=\"MathJax-Span-64\" class=\"mi\">n<\/span><\/span><\/span><\/span><\/span> the level-<span id=\"MathJax-Element-9-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-65\" class=\"math\"><span id=\"MathJax-Span-66\" class=\"mrow\"><span id=\"MathJax-Span-67\" class=\"mi\">n<\/span><\/span><\/span><\/span> vertices of <span id=\"MathJax-Element-10-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-68\" class=\"math\"><span id=\"MathJax-Span-69\" class=\"mrow\"><span id=\"MathJax-Span-70\" class=\"mi\">T<\/span><\/span><\/span><\/span>. Assume <span id=\"MathJax-Element-11-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-71\" class=\"math\"><span id=\"MathJax-Span-72\" class=\"mrow\"><span id=\"MathJax-Span-73\" class=\"mi\">M<\/span><\/span><\/span><\/span> has a real second-largest (in absolute value) eigenvalue <span id=\"MathJax-Element-12-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-74\" class=\"math\"><span id=\"MathJax-Span-75\" class=\"mrow\"><span id=\"MathJax-Span-76\" class=\"mi\">\u03bb<\/span><\/span><\/span><\/span> with corresponding real eigenvector <span id=\"MathJax-Element-13-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-77\" class=\"math\"><span id=\"MathJax-Span-78\" class=\"mrow\"><span id=\"MathJax-Span-79\" class=\"mi\">\u03bd<\/span><span id=\"MathJax-Span-80\" class=\"mo\">\u2260<\/span><span id=\"MathJax-Span-81\" class=\"mn\">0<\/span><\/span><\/span><\/span>. Letting <span id=\"MathJax-Element-14-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-82\" class=\"math\"><span id=\"MathJax-Span-83\" class=\"mrow\"><span id=\"MathJax-Span-84\" class=\"msubsup\"><span id=\"MathJax-Span-85\" class=\"mi\">\u03c3<\/span><span id=\"MathJax-Span-86\" class=\"mi\">v<\/span><\/span><span id=\"MathJax-Span-87\" class=\"mo\">=<\/span><span id=\"MathJax-Span-88\" class=\"msubsup\"><span id=\"MathJax-Span-89\" class=\"mi\">\u03bd<\/span><span id=\"MathJax-Span-90\" class=\"texatom\"><span id=\"MathJax-Span-91\" class=\"mrow\"><span id=\"MathJax-Span-92\" class=\"msubsup\"><span id=\"MathJax-Span-93\" class=\"mi\">\u03be<\/span><span id=\"MathJax-Span-94\" class=\"mi\">v<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>, we consider the following root-state estimator, which was introduced by Mossel and Peres (2003) in the context of the &#8220;recontruction problem&#8221; on trees:<\/p>\n<div class=\"MathJax_Display\"><span id=\"MathJax-Element-15-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-95\" class=\"math\"><span id=\"MathJax-Span-96\" class=\"mrow\"><span id=\"MathJax-Span-97\" class=\"msubsup\"><span id=\"MathJax-Span-98\" class=\"mi\">S<\/span><span id=\"MathJax-Span-99\" class=\"mi\">n<\/span><\/span><span id=\"MathJax-Span-100\" class=\"mo\">=<\/span><span id=\"MathJax-Span-101\" class=\"mo\">(<\/span><span id=\"MathJax-Span-102\" class=\"mi\">b<\/span><span id=\"MathJax-Span-103\" class=\"mi\">\u03bb<\/span><span id=\"MathJax-Span-104\" class=\"msubsup\"><span id=\"MathJax-Span-105\" class=\"mo\">)<\/span><span id=\"MathJax-Span-106\" class=\"texatom\"><span id=\"MathJax-Span-107\" class=\"mrow\"><span id=\"MathJax-Span-108\" class=\"mo\">\u2212<\/span><span id=\"MathJax-Span-109\" class=\"mi\">n<\/span><\/span><\/span><\/span><span id=\"MathJax-Span-110\" class=\"munderover\"><span id=\"MathJax-Span-111\" class=\"mo\">\u2211<\/span><span id=\"MathJax-Span-112\" class=\"texatom\"><span id=\"MathJax-Span-113\" class=\"mrow\"><span id=\"MathJax-Span-114\" class=\"mi\">x<\/span><span id=\"MathJax-Span-115\" class=\"mo\">\u2208<\/span><span id=\"MathJax-Span-116\" class=\"msubsup\"><span id=\"MathJax-Span-117\" class=\"mi\">L<\/span><span id=\"MathJax-Span-118\" class=\"mi\">n<\/span><\/span><\/span><\/span><\/span><span id=\"MathJax-Span-119\" class=\"msubsup\"><span id=\"MathJax-Span-120\" class=\"mi\">\u03c3<\/span><span id=\"MathJax-Span-121\" class=\"mi\">x<\/span><\/span><span id=\"MathJax-Span-122\" class=\"mo\">.<\/span><\/span><\/span><\/span><\/div>\n<p>As noted by Mossel and Peres, when <span id=\"MathJax-Element-16-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-123\" class=\"math\"><span id=\"MathJax-Span-124\" class=\"mrow\"><span id=\"MathJax-Span-125\" class=\"mi\">b<\/span><span id=\"MathJax-Span-126\" class=\"msubsup\"><span id=\"MathJax-Span-127\" class=\"mi\">\u03bb<\/span><span id=\"MathJax-Span-128\" class=\"mn\">2<\/span><\/span><span id=\"MathJax-Span-129\" class=\"mo\">><\/span><span id=\"MathJax-Span-130\" class=\"mn\">1<\/span><\/span><\/span><\/span> (the so-called Kesten-Stigum reconstruction phase) the quantity <span id=\"MathJax-Element-17-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-131\" class=\"math\"><span id=\"MathJax-Span-132\" class=\"mrow\"><span id=\"MathJax-Span-133\" class=\"msubsup\"><span id=\"MathJax-Span-134\" class=\"mi\">S<\/span><span id=\"MathJax-Span-135\" class=\"mi\">n<\/span><\/span><\/span><\/span><\/span> has uniformly bounded variance. Here, we give bounds on the moment-generating functions of <span id=\"MathJax-Element-18-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-136\" class=\"math\"><span id=\"MathJax-Span-137\" class=\"mrow\"><span id=\"MathJax-Span-138\" class=\"msubsup\"><span id=\"MathJax-Span-139\" class=\"mi\">S<\/span><span id=\"MathJax-Span-140\" class=\"mi\">n<\/span><\/span><\/span><\/span><\/span> and <span id=\"MathJax-Element-19-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-141\" class=\"math\"><span id=\"MathJax-Span-142\" class=\"mrow\"><span id=\"MathJax-Span-143\" class=\"msubsup\"><span id=\"MathJax-Span-144\" class=\"mi\">S<\/span><span id=\"MathJax-Span-145\" class=\"mn\">2<\/span><span id=\"MathJax-Span-146\" class=\"mi\">n<\/span><\/span><\/span><\/span><\/span> when <span id=\"MathJax-Element-20-Frame\" class=\"MathJax\" tabindex=\"0\"><span id=\"MathJax-Span-147\" class=\"math\"><span id=\"MathJax-Span-148\" class=\"mrow\"><span id=\"MathJax-Span-149\" class=\"mi\">b<\/span><span id=\"MathJax-Span-150\" class=\"msubsup\"><span id=\"MathJax-Span-151\" class=\"mi\">\u03bb<\/span><span id=\"MathJax-Span-152\" class=\"mn\">2<\/span><\/span><span id=\"MathJax-Span-153\" class=\"mo\">><\/span><span id=\"MathJax-Span-154\" class=\"mn\">1<\/span><\/span><\/span><\/span>. Our results have implications for the inference of evolutionary trees.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Consider a Markov chain (\u03bev)v\u2208V\u2208[k]V on the infinite b-ary tree T=(V,E) with irreducible edge transition matrix M, where b\u22652, k\u22652 and [k]={1,&#8230;,k}. We denote by Ln the level-n vertices of T. Assume M has a real second-largest (in absolute value) eigenvalue \u03bb with corresponding real eigenvector \u03bd\u22600. Letting \u03c3v=\u03bd\u03bev, we consider the following root-state estimator, [&hellip;]<\/p>\n","protected":false},"featured_media":0,"template":"","meta":{"msr-url-field":"","msr-podcast-episode":"","msrModifiedDate":"","msrModifiedDateEnabled":false,"ep_exclude_from_search":false,"_classifai_error":"","msr-author-ordering":null,"msr_publishername":"Institute of Mathematical Statistics","msr_publisher_other":"","msr_booktitle":"","msr_chapter":"","msr_edition":"","msr_editors":"","msr_how_published":"","msr_isbn":"","msr_issue":"","msr_journal":"Electronic Communications in 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