Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Incoherent value for partial derivative

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91050] Incoherent value for partial derivative
  • From: Miguel <misvrne at gmail.com>
  • Date: Mon, 4 Aug 2008 03:26:32 -0400 (EDT)

Let

In[1]: g[x_]:=3x^2+5x;
FullForm[g'[x]]

Out[1]: Plus[5,Times[6,x]]

In[2]: g'[2]
Out[2]: 17

Mathematica works fine and the result is correct. First, it executes
the derivation and then the delayed substitution/assignation. But for
partial derivative Mathematica works different way (not correspondig
to FullForm

In[3]: f[x_,y_]:=x^2+x y^2;
FullForm[\!\(
\*SubscriptBox[\(\[PartialD]\), \(x\)]\ \(f[x, y]\)\)]

Out[3]: Plus[Times[2,x],Power[y,2]]

In[4]: \!\(
\*SubscriptBox[\(\[PartialD]\), \(x\)]\ \(f[1, 2]\)\)
Out[4]: 0

I dont understand the reason.




  • Prev by Date: Re: Text search within a documentation page?
  • Next by Date: Re: Performance of Array Addition
  • Previous by thread: Re: Text search within a documentation page?
  • Next by thread: Re: Incoherent value for partial derivative