Ever since version 6 of Mathematica was released (way back in 2007) I have received dozens of queries from users at my University saying something along the lines of ‘Plotting no longer works in Mathematica’ or ‘If I wrap my plot in a Do loop then I get no output.\u00a0 The user usually goes on to say that it worked perfectly well in pre-v6 versions of Mathematica, is clearly a bug and could I please file a bug report with Wolfram Research?<\/p>\n
It’s not a bug….it’s a feature!<\/p>\n
If you have googled your way here and just want a fast solution to your problem then here goes.\u00a0 I assume that you have code that looks like this<\/p>\n
Do[\r\n Plot[Cos[n x], {x, -Pi, Pi}]\r\n , {n, 1, 3}\r\n ]<\/pre>\nand you were expecting to get a set of nice plots (in this case 3) – one plot for each iteration of your loop. Instead, Mathematica 6 or above is giving you nothing…nada…zip! There are several ways you can ‘fix’ this and I am going to show you two. Option 1 is to wrap your Plot Command with Print<\/p>\n
Do[\r\n Print[Plot[Cos[n x], {x, -Pi, Pi}]]\r\n , {n, 1, 3}\r\n ]<\/pre>\nOption 2 is to use Table instead of Do<\/p>\n
Table[\r\n Plot[Cos[n x], {x, -Pi, Pi}]\r\n , {n, 1, 3}\r\n ]<\/pre>\nI am imaging that the average googler has now disappeared having got what they came for but some of you are possibly wondering why the above two ‘fixes’ work.\u00a0 Here’s my attempt at an explanation.<\/p>\n
Old versions of Mathematica (v5.2 and below) treated graphics very differently to the way that Mathematica works today. The output of a command such as Plot[] used to contain two parts – the first was a Graphics object which looked a bit like the following in the notebook front end<\/p>\n
– Graphics –<\/strong><\/p>\nThis was the OutputForm of the actual symbolic result of the Plot[] command. The second part – the actual visualization of the plot – was effectively just a side effect that happened to be what us humans actually wanted.<\/p>\n
In version 6 and above, the OutputForm of a Graphics object is its visualisation which makes a lot more sense then just – Graphics –<\/strong>. The practical upshot of this is that there is now no need for a ‘side effect’ since the visualization of the plot IS the output.\u00a0 If you are confused then this bit is explained much more eloquently in an old Wolfram Blog post<\/a>.<\/p>\nThat’s the first part of the story regarding plots in loops.\u00a0 The second piece of the puzzle is to know that when you wrap a Mathematica expression in a Do loop then you suppress its output but you don’t suppress any side effects<\/strong>.\u00a0 In version 5.2 the plot is a side effect and so it gets displayed on each iteration of the loop.\u00a0 In version 6 and above, the plot is the output and so gets suppressed unless you explicitly ask for it to be displayed using Print[].<\/p>\nDoes this help clear things up?\u00a0 Comments welcomed.<\/p>\n","protected":false},"excerpt":{"rendered":"
Ever since version 6 of Mathematica was released (way back in 2007) I have received dozens of queries from users at my University saying something along the lines of ‘Plotting no longer works in Mathematica’ or ‘If I wrap my plot in a Do loop then I get no output.\u00a0 The user usually goes on […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[8,7],"tags":[],"class_list":["post-2200","post","type-post","status-publish","format-standard","hentry","category-mathematica","category-programming"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p3swhs-zu","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/2200","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2200"}],"version-history":[{"count":8,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/2200\/revisions"}],"predecessor-version":[{"id":2208,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/2200\/revisions\/2208"}],"wp:attachment":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2200"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2200"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2200"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}