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Re: define a function with variable coefficients

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105882] Re: define a function with variable coefficients
  • From: dh <dh at metrohm.com>
  • Date: Wed, 23 Dec 2009 02:41:20 -0500 (EST)
  • References: <hgq23i$g8d$1@smc.vnet.net>


Hi Adong,

"_" and "^" are a reserved characters and can not  be used as a 

super/subscripts. Instead use "Subscript" and "Superscript":



f[z_, t_] = Sum[Subscript[a, j][t]* Superscript[z, j], {j, 1, n}]

f[x, y]



Daniel





Andong He wrote:

> Hi,

> I wanna define f[z_, t_] = Sum[a_j*z^j, {j, 1, n}], where I use "_j" and "^j" to denote the subscript and superscript. It gives a f as a series, which is fine.

> 

> But if I want a_j to be functions of t, say

> f[z_, t_] = Sum[a_j[t]*z^j, {j, 1, n}],

> it yields something which doesn't make sense. For example, it has terms a_(1+n)[t] and a_(2+n)[t] which are not even defined in my expression for f!!!

> 

> Can anyone help me figure out what's going on? Thanks!

> 




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