Help to build a function to approximate a expression when X >> Y

I am not sure I understand what you mean, but perhaps something like

      taylor( EXPR, x, inf,1, y, inf, 1)

is what you want? (if you're interested in non-linear terms, change 1 to 2
or more)

Another way (pretty much equivalent, but perhaps more intuitive) is

     ex1: subst( x*a, y, EXPR );
     ex2: taylor(ex1,a,0,1);
     subst(y/x,a,ex2);

       -s


On 10/2/07, Javier Sanchez <javier_home at terra.es> wrote:
>
> I do have expressions of the form
>
> (a + b + c + d)*x + (d + e )*y +f
>
> I 'd like to approximate these expressions assuming x >> y in the form
>
> (a + b + c)*x + (d + e )*y +f
>