Integration problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg27417] Integration problem*From*: "drek" <drek1976 at yahoo.com>*Date*: Sun, 25 Feb 2001 00:53:41 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi all, I am presently experiencing some problems with the use of integration in Mathematica, and I do not understand what could be wrong. I defined 2 functions as follow: Tx1[i_] := ((1/a)*(1 - Abs[x - i*a]/a))*(UnitStep[x - (i - 1)*a] - UnitStep[x - (i + 1)*a]) Ty1[j_] := (UnitStep[y - (j - 1)*b] - UnitStep[y - j*b]) where a, b are any assigned real values. I then formed a matrix as follows: JsxT := Table[Ty1[p]*Tx1[m], {m, L - 1}, {p, W}] which is then followed by: JsxSum = Sum[JsxT[[m,p]], {m, 1, 4}, {p, 1, 9}] I then try to integrate JsxSum with respect to x and y in the following way: Integrate[JsxSum, {x, 0, a}, {y, 0, b}] When Mathematica (I'm using version 4) tries to work out this last expression, it outputs the following message: "Unique::usym : -0.43661971830985913 is not a symbol or a valid sumbol name" before giving an output. This problem occurs whatever values I may use for a and b. Does someone know why? Thanks for any help rendered.