Comments on: How to find all roots of a function in two variables?
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables/
Comments on Ask MetaFilter post How to find all roots of a function in two variables?Sun, 15 Aug 2010 08:40:43 -0800Sun, 15 Aug 2010 08:40:43 -0800en-ushttp://blogs.law.harvard.edu/tech/rss60Question: How to find all roots of a function in two variables?
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables
I've got a long function with two variables, encoding - I suspect - a hidden message. Most likely, the message is somehow encoded in the function's roots. Is there any good software to plot a function in two dimensions and only show the points where it evaluates to zero? <br /><br /> I've tried gnuplot and octave, but I couldn't get them to show what I wanted.<br>
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Do you have any ideas? Software for Linux or Windows is appreciated.<br>
Other ideas how to encode a message in a function?post:ask.metafilter.com,2010:site.162318Sun, 15 Aug 2010 08:18:45 -0800TritonmathsteganographyfunctionplotrootresolvedBy: RustyBrooks
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2330914
Seems like a contour plot would do it, if you could control the coloring, to show the area around 0 to be red or something?comment:ask.metafilter.com,2010:site.162318-2330914Sun, 15 Aug 2010 08:40:43 -0800RustyBrooksBy: JumpW
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2330954
I think any stats package would do this for you. R is free and powerful, you might try the function 'contour3d':<br>
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<a href="http://rss.acs.unt.edu/Rdoc/library/misc3d/html/contour3d.html">http://rss.acs.unt.edu/Rdoc/library/misc3d/html/contour3d.html</a>comment:ask.metafilter.com,2010:site.162318-2330954Sun, 15 Aug 2010 09:19:18 -0800JumpWBy: Dim Siawns
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2331040
A bit of a kludge in gnuplot might be, given your function f(x,y), to try 'set zrange [-a:a]', with 'a' a very small number, before putting in 'splot f(x,y)'. Gnuplot should then only display those parts of the function near zero. Or alternatively, tell us what the function is and see if the hivemind can work it out!comment:ask.metafilter.com,2010:site.162318-2331040Sun, 15 Aug 2010 11:13:21 -0800Dim SiawnsBy: Netzapper
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2331138
Please give us the function! That sounds like a wonderful afternoon's diversion.comment:ask.metafilter.com,2010:site.162318-2331138Sun, 15 Aug 2010 12:56:35 -0800NetzapperBy: Dr Dracator
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2331157
Try googling for implicit curves - what you want to do is draw the implicit curve f(x,y)=0. Gnuplot can handle those, have you checked <a href="http://t16web.lanl.gov/Kawano/gnuplot/implicit/solve-e.html">this page</a> out?comment:ask.metafilter.com,2010:site.162318-2331157Sun, 15 Aug 2010 13:13:32 -0800Dr DracatorBy: onalark
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2331730
Have you tried simply plotting the function? I ask because it could be an instance of <a href="http://ask.metafilter.com/56216/How-does-Tupper-turn-a-number-into-a-map">Tupper's Self-Referential Formula</a> being used to convey some other information.<br>
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You first need to be able to identify all the roots of the function. For a general function in two variables this could be very, very hard. If it is polynomial (or you can find a reasonable polynomial approximation) you have a shot, using the <a href="http://www.math.uic.edu/~jan/srvart/node4.html">homotopy continuation method</a>. On the other hand, if it uses transcendental functions you will probably need a more careful analysis.<br>
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This sounds like an interesting problem, you have already identified and tagged the class (steganography), I don't have any good further advice for you.comment:ask.metafilter.com,2010:site.162318-2331730Sun, 15 Aug 2010 22:57:42 -0800onalarkBy: Triton
http://ask.metafilter.com/162318/How-to-find-all-roots-of-a-function-in-two-variables#2331805
Thank you for your advice!<br>
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I'll try the contour plot later. The function is indeed polynomial.<br>
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I most likely won't need all roots, just the ones within a certain range.<br>
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to Netzapper:<br>
I understand your curiosity, but if it is indeed a hidden message, it is probably meant to be read by me.<br>
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to Dr. Dracator:<br>
I haven't! Thank you, I got lost in the gnuplot manual before, this definitely looks promising!comment:ask.metafilter.com,2010:site.162318-2331805Mon, 16 Aug 2010 03:45:16 -0800Triton