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Re: Is this a problem in mathematica?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg74627] Re: [mg74615] Is this a problem in mathematica?
*From*: Sseziwa Mukasa <mukasa at jeol.com>
*Date*: Thu, 29 Mar 2007 02:26:58 -0500 (EST)
*References*: <200703280644.BAA20508@smc.vnet.net>
On Mar 28, 2007, at 2:44 AM, traz wrote:
> Let's say I wanna solve this problem:
>
> Determine point(s) on y = x^2 +1 that are
> closest to (0,2).
>
> So in mathematica:
>
> minDist = (x - 0)^2 + (y - 2)^2;
> Minimize[minDist, y == 1 + x^2, {x, y}]
>
> Output will give you: x -> -1/Sqrt[2], y -> 3/2
>
> but x also has another answer: +1/Sqrt[2]. Is this a problem in
> mathematica or can my code be changed to output the other value of
> x for the minimum distance?
Minimize just searches for a minimum, if there are two or more minima
it will only find one at most. If you want general solutions use
Solve to find the minima of the first derivative.
In[4]:=
Solve[D[x\^2 + (1 + x^2 - 2)^2, x]== 0, x]
Out[4]=
{{x -> 0}, {x -> -1/Sqrt[2]}, {x -> 1/Sqrt[2]}}
Checking the distance for each point will allow you to reject the
point at 0 as a minimum.
Regards,
Ssezi
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