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MathGroup Archive 2005

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Re: Plotting numerical derivatives

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53922] Re: Plotting numerical derivatives
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Fri, 4 Feb 2005 04:11:17 -0500 (EST)
  • Organization: The University of Western Australia
  • References: <ctnik9$f0e$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <ctnik9$f0e$1 at smc.vnet.net>, "plizak" <plizak at gmail.com> 
wrote:

> I'm trying to differentiate a function of the form
> 
> FTD[t1_, t2_] := a function of t1 and t2
> 
> I can get the derivative fine by using:
> ND[ND[Fun[t1, t2 ], {t1, 1}, 200000], {t2, 1}, 200000 ]

To require ND in NumericalMath`NLimit`, I assume that FTD must be a 
functino for which it is difficult or impossible to analytically compute 
the derivative? Is this the case? Otherwise you could just enter

   Derivative[1, 1][Fun][200000, 200000]

> However, I'd like to plot it in a 3D plot, and it just doesn't want to
> work.  I get a flat plot with value 0.  The code I tried to use is:
> 
> Plot3D[ND[ND[Fun[t1, t2 ]  , {t1, 1}, a]  , {t2, 1}, b ], {a, 1,
> 500000}, {b, 1, 500000}]
> 
> Any tips on getting this to plot would be greatly appreciated!

Plot3D has the HoldAll attribute so you would need to wrap an Evaluate[] 
around the first argument.

Cheers,
Paul

-- 
Paul Abbott                                   Phone: +61 8 6488 2734
School of Physics, M013                         Fax: +61 8 6488 1014
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Crawley WA 6009                      mailto:paul at physics.uwa.edu.au 
AUSTRALIA                            http://physics.uwa.edu.au/~paul


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