{"id":801,"date":"2009-11-23T18:01:34","date_gmt":"2009-11-23T17:01:34","guid":{"rendered":"http:\/\/www.walkingrandomly.com\/?p=801"},"modified":"2010-08-27T14:12:42","modified_gmt":"2010-08-27T13:12:42","slug":"a-random-collection-of-bugs-in-mathematica-7-and-7-0-1","status":"publish","type":"post","link":"https:\/\/walkingrandomly.com\/?p=801","title":{"rendered":"A random collection of bugs in Mathematica 7 and 7.0.1"},"content":{"rendered":"

There was a discussion recently on comp.soft-sys.math.mathematica<\/a> about maintaining a user-led Mathematica bug list<\/a> and various solutions were proposed.\u00a0 I have no desire (and certainly no time) to even try to maintain a ‘proper’ bug database for Mathematica but I am interested in maintaining a list of bugs that I personally find interesting<\/strong> and that I would like to see explained or fixed.<\/p>\n

This post is that list.<\/p>\n

First – some answers to potential questions.<\/p>\n

Why are you doing this?\u00a0 I thought you liked Mathematica.<\/strong><\/p>\n

I love Mathematica but, like all pieces of software, it is not perfect.\u00a0 I find (some of) the imperfections interesting and since I get lots of hits from google every month from people looking for bugs in MATLAB, Mathematica, Maple, Mathcad etc then I assume that I am not alone.\u00a0 Every bug that I discuss here will be submitted to Wolfram Research and I will also update the page when the bug gets fixed.<\/p>\n

I emailed\/wrote a comment about a bug and you haven’t included it in the list. Why?
\n<\/strong><\/p>\n

Sorry about that – please don’t take it personally.\u00a0 I am low on time and may not have managed to verify the ‘bug’ or maybe it just didn’t tickle my fancy.\u00a0 It’s also possible that I simply don’t understand the problem you are referring to and I will not post anything on here that I don’t at least think<\/strong> I understand.\u00a0 Remember – I’m not trying to keep a list of all<\/strong> Mathematica bugs – just some of the ones that I find interesting.<\/p>\n

One of the ‘bugs’ you posted is not a bug – you just misunderstood the situation.<\/strong><\/p>\n

Oops, sorry!\u00a0 Please educate me so I can update it.<\/p>\n

I think I have found a bug in Mathematica – what should I do?<\/strong><\/p>\n

In the first instance I suggest you post it to comp.soft-sys.math.mathematica<\/a> – there are plenty of people there who know a lot about Mathematica and they (probably) will let you know if you really have found a bug or not. If everyone suspects that it is a bug then your next step is to report it to Wolfram<\/a>.\u00a0 Finally, if you think I’d like to know about it then feel free to leave a comment to this post or email me<\/a>.<\/p>\n

FullSimplify bug 1<\/strong><\/h3>\n
Clear[n];\r\nFullSimplify[n Exp[-n * 0.], Element[n, Integers]]<\/pre>\n
expected output:<\/p>\n
n<\/pre>\n
actual output:<\/p>\n
n\/2<\/pre>\n
original source – here<\/a>.<\/p>\n
Integrate bug 1<\/strong><\/h3>\n
Integrate[k^2 (k^2 - 1)\/((k^2 - 1)^2 + x^2)^(3\/2), {k, 0, Infinity},Assumptions -> x > 0]<\/pre>\n
Expected output:<\/p>\n
1\/2*1\/(1+x^2)^(1\/4)*EllipticK(1\/2*2^(1\/2)*(((1+x^2)^(1\/2)+1)\/(1+x^2)^(1\/2))^(1\/2))<\/pre>\n
Actual output:<\/p>\n
EllipticK[(2*x)\/(-I + x)]\/(2*Sqrt[-1 - I*x])<\/pre>\n
Note that although the integrand is real for all k, Mathematica gives a complex result which is clearly wrong.\u00a0 Original source – here<\/a>.<\/p>\n
Limit bug 1<\/strong><\/h3>\n
Limit[EllipticTheta[3, 0, x], x -> 1, Direction -> 1]<\/pre>\n
Expected Output:<\/p>\n
Infinity<\/pre>\n
Actual Output:<\/p>\n
0<\/pre>\n
Original Source: here<\/a><\/p>\n
NetworkFlow bug<\/h3>\n
The following code should complete in less than a second.<\/p>\n
\r\n<< \"Combinatorica`\"\r\nNetworkFlow[CompleteGraph[4, 4], 1, 8]\r\n<\/pre>\n
but in Mathematica 7.0.1 (tested on Windows and Linux) it never completes and hogs a CPU indefinitely. Wolfram are aware of this one and it should be fixed in the next release.  Thanks to G\u00e1bor Megyesi of Manchester University for sending me this one.<\/p>\n
Feel free to let me know of others that you find but please bear in mind the points at the beginning of this post.<\/p>\n","protected":false},"excerpt":{"rendered":"
There was a discussion recently on comp.soft-sys.math.mathematica about maintaining a user-led Mathematica bug list and various solutions were proposed.\u00a0 I have no desire (and certainly no time) to even try to maintain a ‘proper’ bug database for Mathematica but I am interested in maintaining a list of bugs that I personally find interesting and that […]<\/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],"tags":[],"class_list":["post-801","post","type-post","status-publish","format-standard","hentry","category-mathematica"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p3swhs-cV","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/801","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=801"}],"version-history":[{"count":23,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/801\/revisions"}],"predecessor-version":[{"id":2841,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/801\/revisions\/2841"}],"wp:attachment":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=801"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=801"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=801"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}