• To: mathgroup at smc.vnet.net
• Subject: [mg84295] Re: quadratic multiplication
• From: KFUPM <hussain.alqahtani at gmail.com>
• Date: Mon, 17 Dec 2007 19:22:12 -0500 (EST)
• References: <fk2v35\$n96\$1@smc.vnet.net> <fk5akt\$5jc\$1@smc.vnet.net>

```On Dec 17, 11:05 am, dh <d... at metrohm.ch> wrote:
> Hi,
>
> we may create a rule that sets all products of u^s to zero:
>
> mem[y_]:=MemberQ[{u1,u2,u3,u4,u5,u6},y];
>
> rules={y1_ y2_/;mem[y1]&&mem[y2]->0,y_^_/;mem[y]->0};
>
> here is an example:
>
> c1 u1+c2 u2+ c15 u1 u5 + c146 u1 u4 u6 /. rules
>
> hope this helps, Daniel
>
>
>
> KFUPM wrote:
> > Dear all
>
> > I have a very large expression which involves the multiplication of
> > these variables:
>
> > var ={u1,u2,u3,u4,u5,u6} with some other constants. In the expression,
> > i want to suppress any quadratic or higher order multiplication of
> > these varibles , e.g u1*u5  or u1*u4*u6 should be zero. And since, my
> > expression is huge, i want to do this automatically. Any help in this
> > regard is highly appreciated.
>
> > Sincererly yours,
>
> > HMQ- Hide quoted text -
>
> - Show quoted text -

The rule didn't work for this term:

Out[103]=
\!\(\*
RowBox[{\(5\/2\), " ", \(b\^4\), " ", \(x[2]\^4\), " ",
RowBox[{
SuperscriptBox["u11",
TagBox[\((1, 0, 0)\),
Derivative],
MultilineFunction->None], "[", \(x[1], x[3], t\), "]"}], " ",
RowBox[{
SuperscriptBox["u13",
TagBox[\((1, 0, 0)\),
Derivative],
MultilineFunction->None], "[", \(x[1], x[3], t\), "]"}]}]\)

Please note that b is a constant. So the varibles are only u11 u13.

I appreciate your help in this regard.

Thanks in anticipation.

```

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