<![CDATA[Any command/tool for generating a quadratic surface(quadric) given 9 points?]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points
Tue, 09 Apr 2019 13:24:41 +0000Fri, 05 Apr 2019 22:27:45 +0000Zend_Feed<![CDATA[I'm sure I've seen that using GeoGebra's matrix commands (but I can't find it :( ) Hopefully this helps: https://math.stackexchange....]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-258984
Mon, 08 Apr 2019 06:32:01 +0000<![CDATA[How's this? Exact for 6 points: https://www.geogebra.org/m/fqfe5trp (it can be made more efficient if the points only move vertically as M_A will then be constant) I think you can probably use the SVD command if you want "best fit" through eg 9 points https://wiki.geogebra.org/e...]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-258986
Mon, 08 Apr 2019 07:06:50 +0000<![CDATA[Hi Michael, I made a try to calc quadrik by f(x,y)=Sum(m3 {x², y², x y, x, y, 1}) can you check the result too? got a list. why? BTW my ipad do not give me the keyboard using online app - had to download the file to work with, great work! I remember there was a post to this?]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-258988
Mon, 08 Apr 2019 08:49:18 +0000<![CDATA[I think this is OK for 9 points (maybe you can check against your Mathematica answers to verify) https://www.geogebra.org/m/dwsk5nwg]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-258990
Mon, 08 Apr 2019 08:48:17 +0000<![CDATA[I think that's OK. Try Sum(Sum(m3 {x², y², x y, x, y, 1}))]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-258992
Mon, 08 Apr 2019 08:50:50 +0000<![CDATA[Sorry, didn't use enough terms. I've updated https://www.geogebra.org/m/fqfe5trp so it's now exact for 9 points :)]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-258998
Mon, 08 Apr 2019 10:50:59 +0000<![CDATA[I used the CAS to substitute into the general equation of a quadric the coordinates of the nine points, solve the resulting system of equations and again substitute the solution into the equation. I thus obtained the equation of the quadric, see here the result: https://www.geogebra.org/m/mxpdmt4n]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-259000
Mon, 08 Apr 2019 14:13:14 +0000<![CDATA[with brute force. but I am afraid the PC crashes]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-259006
Mon, 08 Apr 2019 13:38:03 +0000<![CDATA[Works well here (also in browser!)]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-259008
Mon, 08 Apr 2019 14:15:07 +0000<![CDATA[... and much shorter solutions from Zbynek Fit({A, B, C, D, E, F, G, H, I}, {1, x, y, x y, x², y²})
Fit({A, B, C, D, E, F, G, H, I}, {1, x, y, x y, x², y², x² y, x y², x² y²})]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-259010
Mon, 08 Apr 2019 16:10:10 +0000<![CDATA[... and what the original poster actually wants I think from Mathieu :) https://www.geogebra.org/m/xqkwgcan]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-259028
Tue, 09 Apr 2019 06:03:51 +0000<![CDATA[awesome but they fail when (0,0,0) is in quadric (mine too) this problem was also implementing conic]]>
https://help.geogebra.org/topic/any-commandtool-for-generating-a-quadratic-surfacequadric-given-9-points#comment-259040
Tue, 09 Apr 2019 13:25:43 +0000