Re: V6 evaluation inside Table and plot
- To: mathgroup at smc.vnet.net
- Subject: [mg76650] Re: V6 evaluation inside Table and plot
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Fri, 25 May 2007 06:34:06 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <f33onq$l4v$1@smc.vnet.net>
Gerry Flanagan wrote:
> Define a simple function
>
> In[7]:= f = Function[{x}, x^3]
>
> Out[7]= Function[{x}, x^3]
>
> Taking two derivatives works as it should
>
> In[2]:= f''[x]
>
> I was converting some packages to work with V6, and immediately ran into
> some evaluation issues I don't understand. It looks like forms like
> f''[x] (derivative) are evaluated differently inside of Table and Plot
> than outside.
>
> Out[2]= 6 x
>
> But this does not?
>
> In[20]:= Table[f''[x], {x, 0, 1, .2}]
>
> Out[20]= {0, 0, 0, 0, 0, 0}
>
> Strangely, this works
>
> In[4]:= Table[f'[x], {x, 0, 1, .2}]
>
> Out[4]= {0., 0.12, 0.48, 1.08, 1.92, 3.}
>
> Determining the derivative outside the Table makes it work again.
>
> In[12]:= g = f'';
>
> In[21]:= tmp = Table[g[x], {x, 0, 1, .2}]
>
> Out[21]= {0., 1.2, 2.4, 3.6, 4.8, 6.}
>
> Gerry Flanagan
>
Note that the second differentiation will take place as expected if you
wrapped your function(s) within Evaluate (or set the option Evaluated to
True in the Plot command).
Clear[f]
f = Function[{x}, x^3];
Table[Evaluate[{f'[x], f''[x]}], {x, 0, 1, .2}]
Plot[Evaluate[{f'[x], f''[x]}], {x, 0, 1, .2}]
Plot[{f'[x], f''[x]}, {x, 0, 1, .2}, Evaluated -> True]
Regards,
Jean-Marc