Creating function from R^n -> R with large n

Dear all,
I am working with functions from R^n to R with n quite large (fromm n=100 to n=1000)
Dummy example:
for f(x)=(x+y)^2+(x+y)^2+...+(x+y)^2 I create the functions this way:
const ExprNode* e;
Variable x(2, "x");
e = &(sqr(x[1] + x[0]));
for (unsigned int i = 1; i < 1000; i++)
   e = &(*e + sqr(x[1]+ x[0]));
Function *f= new Function(x, *e, "f");
However as i grows, each loop execution takes longer and longer, probably due to the concatenation.
Is there a smarter/faster way to programmatically create this type of function?
Jeremy Nicola

Hi Jérémy,
When you apply the "+" operator between two expressions, they are scanned to detect  subexpressions that are in common. This takes a time which is linear in the size of each sub-expression.
That is why the loop takes longer and longer, this is because of the "+" operator.
So the whole loop has a quadratic complexity. To circumvent this in your example, you can simply build the expression "blockwise", like this:
    int N=10000;

    for (unsigned int i = 1; i < log2(N)+1; i++)
       e = &(*e + *e);
This will go much faster.