{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T14:35:34Z","timestamp":1787322934204,"version":"3.56.0"},"reference-count":33,"publisher":"Society for Industrial & Applied Mathematics (SIAM)","issue":"1","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["SIAM J. Imaging Sci."],"published-print":{"date-parts":[[2012,1]]},"abstract":"<jats:p>This paper deals with the computation of sectional curvature for the manifolds of N landmarks (or feature points) in D dimensions, endowed with the Riemannian metric induced by the group action of diffeomorphisms. The inverse of the metric tensor for these manifolds (i.e., the cometric), when written in coordinates, is such that each of its elements depends on at most $2D$ of the $ND$ coordinates. This makes the matrices of partial derivatives of the cometric very sparse in nature, thus suggesting solving the highly nontrivial problem of developing a formula that expresses sectional curvature in terms of the cometric and its first and second partial derivatives (we call this Mario's formula). We apply such a formula to the manifolds of landmarks, and in particular we fully explore the case of geodesics on which only two points have nonzero momenta and compute the sectional curvatures of 2-planes spanned by the tangents to such geodesics. The latter example gives insight into the geometry of the full manifolds of landmarks.<\/jats:p>","DOI":"10.1137\/10081678x","type":"journal-article","created":{"date-parts":[[2012,3,16]],"date-time":"2012-03-16T20:14:53Z","timestamp":1331928893000},"page":"394-433","source":"Crossref","is-referenced-by-count":20,"title":["Sectional Curvature in Terms of the Cometric, with Applications to the Riemannian Manifolds of Landmarks"],"prefix":"10.1137","volume":"5","author":[{"given":"Mario","family":"Micheli","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter W.","family":"Michor","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David","family":"Mumford","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"351","published-online":{"date-parts":[[2012,3,15]]},"reference":[{"key":"R1","unstructured":"M. Abramowitz and I. A. 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Jacques Lafontaine,\n                      Riemannian Geometry\n                      , 3rd ed., Springer, Berlin, 2004.","DOI":"10.1007\/978-3-642-18855-8"},{"key":"R11","unstructured":"J. Glaun\u00e8s,\n                      Transport par diff\u00e9omorphismes de points, de mesures et de courants pour la comparaison de formes et l'anatomie num\u00e9rique\n                      , Ph.D. thesis, Universit\u00e9 Paris 13, Villetaneuse, France, 2005."},{"key":"R12","doi-asserted-by":"publisher","DOI":"10.1007\/s11263-008-0141-9"},{"key":"R13","doi-asserted-by":"crossref","unstructured":"J. Glaun\u00e8s, A. Trouv\u00e9, and L. Younes,\n                      Diffeomorphic matching of distributions: A new approach for unlabeled point-sets and sub-manifolds matching\n                      , in Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR '04), Vol. 2, Washington, DC, 2004, pp. 712\u2013718.","DOI":"10.1109\/CVPR.2004.1315234"},{"key":"R14","doi-asserted-by":"publisher","DOI":"10.1023\/B:JMIV.0000011326.88682.e5"},{"key":"R15","doi-asserted-by":"publisher","DOI":"10.1109\/83.855431"},{"key":"R16","unstructured":"J. Jost,\n                      Riemannian Geometry and Geometric Analysis\n                      , 5th ed., Springer, New York, 2008."},{"key":"R17","doi-asserted-by":"publisher","DOI":"10.1112\/blms\/16.2.81"},{"key":"R18","doi-asserted-by":"publisher","DOI":"10.1109\/TPAMI.2004.1262333"},{"key":"R19","doi-asserted-by":"crossref","unstructured":"A. Kriegl and P. W. 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