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.

```

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