{"id":6091,"date":"2026-10-19T09:48:27","date_gmt":"2026-10-19T09:48:27","guid":{"rendered":"https:\/\/phd.hi.is\/doktorsvorn\/doktorsfyrirlestur-i-efnafraedi-olli-pekka-koistinen\/"},"modified":"2026-10-19T09:48:27","modified_gmt":"2026-10-19T09:48:27","slug":"doktorsfyrirlestur-i-efnafraedi-olli-pekka-koistinen","status":"publish","type":"phd_defence","link":"https:\/\/phd.hi.is\/en\/doktorsvorn\/doktorsfyrirlestur-i-efnafraedi-olli-pekka-koistinen\/","title":{"rendered":"Doktorsfyrirlestur \u00ed efnafr\u00e6\u00f0i &#8211; Olli-Pekka Koistinen"},"content":{"rendered":"<div class=\"field-items\">\n<div class=\"field-item even\" property=\"content:encoded\">\n<p><strong>Doktorsefni:<\/strong>\u00a0Olli-Pekka Koistinen<\/p>\n<p><strong>Heiti ritger\u00f0ar:<\/strong>\u00a0Reiknirit til a\u00f0 finna s\u00f6\u00f0ulpunkta og l\u00e1gmarksorkuferla me\u00f0 Gauss a\u00f0hvarfsgreiningu (Algorithms for finding saddle points and minimum energy paths using Gaussian process regression)<\/p>\n<p><strong>Andm\u00e6landi:<\/strong><strong><br \/> <\/strong>Dr. Thomas Bligaard, pr\u00f3fessor vi\u00f0 E\u00f0lisfr\u00e6\u00f0ideild T\u00e6knih\u00e1sk\u00f3la Danmerkur, DTU.<\/p>\n<p><strong>Lei\u00f0beinandi: <\/strong>Dr.\u00a0Hannes J\u00f3nsson, pr\u00f3fessor vi\u00f0 Raunv\u00edsindadeild H\u00e1sk\u00f3la \u00cdslands.<\/p>\n<p><strong>Einnig \u00ed doktorsnefnd:<\/strong><\/p>\n<p>Dr. Aki Vehtari, d\u00f3sent vi\u00f0 T\u00f6lvunarfr\u00e6\u00f0ideild Aalto-h\u00e1sk\u00f3la, Finnlandi.<\/p>\n<p>Dr. Egill Sk\u00falason, pr\u00f3fessor vi\u00f0 I\u00f0na\u00f0arverkfr\u00e6\u00f0i-, v\u00e9laverkfr\u00e6\u00f0i- og t\u00f6lvunarfr\u00e6\u00f0ideild H\u00e1sk\u00f3la \u00cdslands.<strong><\/strong><\/p>\n<\/p>\n<p><strong>Ath\u00f6fn st\u00fdrir:<\/strong>\u00a0Dr. Oddur Ing\u00f3lfsson, pr\u00f3fessor og deildarforseti Raunv\u00edsindadeildar H\u00e1sk\u00f3la \u00cdslands.<\/p>\n<p>Um er a\u00f0 r\u00e6\u00f0a sameiginlega doktorsgr\u00e1\u00f0u vi\u00f0 Aalto-h\u00e1sk\u00f3la og H\u00e1sk\u00f3la \u00cdslands og f\u00f3r v\u00f6rnin fram \u00ed Finnlandi 9. jan\u00faar s\u00ed\u00f0astli\u00f0inn.<\/p>\n<p><strong>\u00c1grip<\/strong><\/p>\n<p>Eiginleika efnahvarfa og annarra umra\u00f0ana at\u00f3ma er h\u00e6gt a\u00f0 kanna me\u00f0 \u00fev\u00ed a\u00f0 sko\u00f0a orkuyfirbor\u00f0i\u00f0, skilgreint sem orka kerfisins sem fall af at\u00f3mhnitunum. Sta\u00f0bundin l\u00e1gm\u00f6rk \u00e1 orkuyfirbor\u00f0inu samsvara \u00e1st\u00f6ndum sem kerfi\u00f0 getur veri\u00f0 \u00ed og l\u00e1gmarksorkuferlar milli \u00feeirra einkenna gang m\u00f6gulegra umra\u00f0ana at\u00f3manna. H\u00e1m\u00f6rk \u00e1 l\u00e1gmarksorkuferlum eru s\u00e9rlega mikilv\u00e6g. \u00deau samsvara fyrsta stigs s\u00f6\u00f0ulpunktum og gefa mat \u00e1 virkjunarorku og \u00fear me\u00f0 hra\u00f0a samsvarandi umr\u00f6\u00f0unar.<\/p>\n<p>L\u00e1gmarksorkuferlar og s\u00f6\u00f0ulpunktar milli tveggja \u00feekktra \u00e1standa eru gjarnan fundnir me\u00f0 \u00edtrekunara\u00f0fer\u00f0um \u00fear sem r\u00f6\u00f0 af \u00edmyndum af kerfinu mynda feril milli endapunktanna og eru f\u00e6r\u00f0ar til \u00feanga\u00f0 til \u00fe\u00e6r liggja \u00e1 l\u00e1gmarksorkuferlinum. F\u00e6rslan \u00ed hverri \u00edtrekun er fundin \u00fat fr\u00e1 stiglunum \u00e1 orkuyfirbor\u00f0inu. S\u00f6\u00f0ulpunktinn er h\u00e6gt a\u00f0 finna me\u00f0 \u00fev\u00ed a\u00f0 f\u00e6ra orkuh\u00e6stu \u00edmyndina \u00ed \u00e1tt stigilsins eftir a\u00f0 \u00fe\u00e6tti hans \u00ed stefnu ferilsins hefur veri\u00f0 sn\u00fai\u00f0 vi\u00f0. \u00deannig f\u00e6rist s\u00fa \u00edmynd upp \u00ed orku a\u00f0 s\u00f6\u00f0ulpunktinum. Ef loka\u00e1stand umr\u00f6\u00f0unarinnar er ekki \u00feekkt er h\u00e6gt a\u00f0 finna fyrsta stigs s\u00f6\u00f0ulpunkt me\u00f0 \u00fev\u00ed a\u00f0 nota par \u00edmynda af kerfinu sem eru \u00fe\u00e9tt saman og myndar tvennu. Henni er sn\u00fai\u00f0 til a\u00f0 finna stefnuna me\u00f0 l\u00e6gstan krappa \u00e1 orkuyfirbor\u00f0inu og h\u00fan s\u00ed\u00f0an f\u00e6r\u00f0 \u00ed \u00e1tt stigulsins eftir a\u00f0 \u00fe\u00e1tturinn \u00ed stefnu l\u00e6gsta krappans hefur veri\u00f0 spegla\u00f0ur. \u00deannig f\u00e6rist tvennan a\u00f0 s\u00f6\u00f0ulpunktinum. \u00deessi a\u00f0fer\u00f0 getur \u00feurft hundru\u00f0 \u00edtrekana og \u00fear e\u00f0 \u00fatreikningar \u00e1 orkustiglinum eru oft \u00feungir er mikilv\u00e6gt a\u00f0 n\u00fdta uppl\u00fdsingar \u00far fyrri \u00edtrekunum eins vel og h\u00e6gt er til a\u00f0 f\u00e6kka \u00edtrekunum. Me\u00f0 \u00fev\u00ed a\u00f0 nota t\u00f6lfr\u00e6\u00f0ileg l\u00edk\u00f6n er h\u00e6gt a\u00f0 b\u00faa til n\u00e1lgun fyrir orkuyfirbor\u00f0i\u00f0 og leita a\u00f0 s\u00f6\u00f0ulpunktinum \u00e1 \u00fev\u00ed yfirbor\u00f0i. Lausnina er h\u00e6gt a\u00f0 sanreyna me\u00f0 frekari \u00fatreikningum \u00e1 orkustiglinum sem s\u00ed\u00f0an er h\u00e6gt a\u00f0 nota til a\u00f0 b\u00e6ta n\u00e1lgunina fyrir n\u00e6stu f\u00e6rslur tvennunnar, o.s.frv.<\/p>\n<p>\u00cd \u00feessari ritger\u00f0 er v\u00e9lr\u00e6nn l\u00e6rd\u00f3mur sem bygg\u00f0ur er \u00e1 Gaussferlaa\u00f0hvarfi nota\u00f0ur til a\u00f0 hra\u00f0a reikningum \u00e1 l\u00e1gmarksorkuferlum og s\u00f6\u00f0ulpunktum. L\u00edk\u00f6n fyrir orkuyfirbor\u00f0i\u00f0 eru b\u00fain til \u00fat fr\u00e1 \u00feekktum gildum \u00e1 orkunni og stiglinum me\u00f0 t\u00f6lfr\u00e6\u00f0ilegum a\u00f0fer\u00f0um Bayes og mat fundi\u00f0 \u00e1 \u00f3vissunni \u00ed l\u00edkaninu sem h\u00e6gt er a\u00f0 n\u00fdta til a\u00f0 \u00e1kve\u00f0a hva\u00f0a punkt er best a\u00f0 reikna \u00ed n\u00e6stu \u00edtrekun.\u00a0 Mismunandi a\u00f0fer\u00f0ir eru \u00fer\u00f3a\u00f0ar b\u00e6\u00f0i til a\u00f0 finna l\u00e1gmarksorkuferla milli tveggja \u00feekktra \u00e1standa og til a\u00f0 finna s\u00f6\u00f0ulpunkt \u00ed n\u00e1grenni gefins upphafspunkts. Reikningar \u00e1 \u00fdmsum mismunandi kerfum s\u00fdna a\u00f0 me\u00f0 \u00feessu m\u00f3ti er h\u00e6gt a\u00f0 f\u00e6kka \u00fatreikningum \u00e1 orkunni og stiglinum mj\u00f6g verulega \u00ed samanbur\u00f0i vi\u00f0 \u00fe\u00e6r a\u00f0fer\u00f0ir sem n\u00fa eru nota\u00f0ar.<\/p>\n<p><strong>Um doktorsefni\u00f0<\/strong><\/p>\n<p>Olli-Pekka Koistinen lauk B.S. pr\u00f3fi \u00ed l\u00edfuppl\u00fdsingat\u00e6kni \u00e1ri\u00f0 2011 fr\u00e1 Aalto-h\u00e1sk\u00f3la \u00ed Espoo \u00ed Finnlandi og MS-pr\u00f3fi \u00ed s\u00f6mu grein fr\u00e1 sama sk\u00f3la \u00e1ri\u00f0 2012. \u00de\u00e1 h\u00f3f hann doktorsn\u00e1m \u00ed reiknifr\u00e6\u00f0i og er n\u00fa a\u00f0 lj\u00faka \u00fev\u00ed n\u00e1mi sem sameiginlegri gr\u00e1\u00f0u \u00ed efnafr\u00e6\u00f0i vi\u00f0 H\u00e1sk\u00f3la \u00cdslands<\/p>\n<\/div><\/div>","protected":false},"featured_media":1846,"template":"","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center 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