Re: Derivatives D[ ] as Functions inside Tables; Need Help!

*To*: mathgroup at smc.vnet.net*Subject*: [mg13182] Re: [mg13102] Derivatives D[ ] as Functions inside Tables; Need Help!*From*: Hugh Walker <hwalker at gvtc.com>*Date*: Mon, 13 Jul 1998 07:42:30 -0400*Sender*: owner-wri-mathgroup at wolfram.com

siegman at ee.stanford.edu wrote: "I'm trying to define a function f1[a,x] and its derivative f2[a,x], where from my point of view x is the independent variable and "a" is a parameter I'll change on different runs. So I write, as a simple example: Remove["Global`*"] f1[a_,x_] :=a Cos[x] + a^2 Sin[x] f1[a,x] f2[a_,x_] := D[f1[a,x],x] f2[a,x] a=2 f1[a,x] f2[a,x] Table[{x, f1[a,x], f2[a.x]} // N, {x,0,4}] // TableForm and everything looks fine -- except the function f2[a,x] will not evaluate inside the Table[ ]. I don't understand this -- help in understanding will be much appreciated." ************************************* There seems to be two problems: (1), the iterator {x,0,4} defaults to integer steps because it is given no stepsize; and (2),the derivitive wrapped by the Table function in the must be evaluated befor a numerical value of x is substituted. Try this. Keep everything the same excepy the last statement. Replace it with Table[{xx, f1[a,xx], f2[a.xx]}xx->x // N, {x,0,4,0.2}] // TableForm Actually, the //N is redundant. Regards. Hugh Walker Professsor Emeritus University of Houston Gnarly Oaks