Re: Newbie: Rotataion2D use problem

• To: mathgroup at smc.vnet.net
• Subject: [mg66724] Re: Newbie: Rotataion2D use problem
• From: Peter Pein <petsie at dordos.net>
• Date: Sat, 27 May 2006 21:03:49 -0400 (EDT)
• References: <e591hh\$35m\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```akil schrieb:
> I have some problems using Mathematica's Rotate2D, it doesnot give the results as I want them
>
> Eample:
>
> a={10, 30}
> b={80., 0.}
> c={38.7689, 0.}
> theta = -0.24497866312686414`
> theta2 = -0.3430239404207034`
> Rotate2D[a, theta, test[[1]]]
> Rotate2D[%, theta2, test[[2]]]
>
> this gives:
> \!\({2.7134309891835002`, 1.7763568394002505`*^-15}\)
>
> While the y-value should be 0 instead of 1.7763568394002505`*^-15.
>
> Anyone know how I can easily fix this, so that I get 0 here instead?
>
> Explanation of reasoning: I need to rotate points about points so that they have the same values, and sometimes like here there are a couple of rotations about points needed, and I always get these weird values, but I reeally need them to be 0 for further research purposes.
>
> (By the way, thanks to all people that replied to my previous post, still need to decide on which one to use, but the problem got a bit harder there, by some complications that are now involved, something to do with clockwise order of found points.)
>
> Akil
>
Hi Akil,

try Chop (see http://documents.wolfram.com/mathematica/functions/Chop) or use exact numbers.

hth,

Peter

```

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