{"id":204,"date":"2007-11-07T00:20:46","date_gmt":"2007-11-07T05:20:46","guid":{"rendered":"http:\/\/www.randomideas.net\/?p=204"},"modified":"2007-11-07T00:20:46","modified_gmt":"2007-11-07T05:20:46","slug":"big-comma-operator-for-multidimensional-indexing","status":"publish","type":"post","link":"http:\/\/randomideas.net\/?p=204","title":{"rendered":"&quot;Big comma&quot; operator for multidimensional indexing?"},"content":{"rendered":"<p>I&#8217;m running into an annoying problem on my dissertation. Since it&#8217;s on tensors, I&#8217;m doing a lot of multidimensional indexing, and I find myself doing a lot of this:<\/p>\n<p>X<sub>i<sub>1<\/sub>,i<sub>2<\/sub>,&#8230;,i<sub>n<\/sub><\/sub>.<\/p>\n<p>Now, Einstein notation lets me avoid writing sums (again, though, I&#8217;m not a fan of it, since there already exists a very nice \u03a3 operator for sums), but it doesn&#8217;t do a thing for <i>sequences<\/i> like this one. In fact, I can&#8217;t find <i>any<\/i> operators that can represent this more concisely.<\/p>\n<p>Now, I can probably treat i as a vector rather than a sequence of scalars, but that might confuse people.<\/p>\n<p>If all else fails, I can probably define something like this:<br \/>\nX<sub><big>,<\/big><sub>j=1<\/sub><sup>n<\/sup><\/sub><\/p>\n<p>, with a big comma in that phrase similar to the huge sigma you use in a sum, but that&#8217;s difficult to represent, as the fact that I need to explain what I was writing demonstrates.<\/p>\n<p>I&#8217;m leaning towards the vector solution, but if someone knows a good notation for this, please let me know.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I&#8217;m running into an annoying problem on my dissertation. Since it&#8217;s on tensors, I&#8217;m doing a lot of multidimensional indexing, and I find myself doing a lot of this: Xi1,i2,&#8230;,in. Now, Einstein notation lets me avoid writing sums (again, though, I&#8217;m not a fan of it, since there already exists a very nice \u03a3 operator [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-204","post","type-post","status-publish","format-standard","hentry","category-research"],"_links":{"self":[{"href":"http:\/\/randomideas.net\/index.php?rest_route=\/wp\/v2\/posts\/204","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/randomideas.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/randomideas.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/randomideas.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/randomideas.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=204"}],"version-history":[{"count":0,"href":"http:\/\/randomideas.net\/index.php?rest_route=\/wp\/v2\/posts\/204\/revisions"}],"wp:attachment":[{"href":"http:\/\/randomideas.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=204"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/randomideas.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=204"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/randomideas.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=204"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}