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