MathGroup Archive 2001

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

Search the Archive

Solving for Sum element

I want to solve for one element in an equation involving long sums.  The
actual equation is of course complicated, but a very simplified example
would be


where I want to solve for a[0].  The solution should be something like

Solve[Sum[a[i], {i, 0, n}] == x, a[0]]

works fine if, for example, n=3, but it returns an empty result for
symbolic n.  Is there a way to tell Solve to assume that n>1 and to solve
accordingly?  The best I've been able to do so far is to explicitly remove
the element I'm interested in from the sum:

In: Solve[a[0] + Sum[a[i], {i, 1, n}] == x, a[0]]
Out: {{a[0] -> x - Sum[a[i], {i, 1, n}]}}

This works nicely, but becomes awkward when I try to solve for more
elements and longer sums.  Thanks.

Ben Jacobson
Illumitech Inc.

  • Prev by Date: Re: Mathematica 4.1 How to.....
  • Next by Date: Re: Graphing Functions for an idiot
  • Previous by thread: Removal of functions
  • Next by thread: RE: Solving for Sum element