simplifying symbolic expression in terms of other variables

This is a simplified problem to illustrate what I need: Given the symbolic expression a^2+b^2+2ab+a+b+1 and the definition x=a+b how do I simplify the symbolic expression to give the answer in terms of x, i.e. x^2+x+1?

I've played around with the symbolic toolbox without success.

Answer 1

[Stefan Wehmeier]

You could also try

    syms a b x
    assume(x== a+b);
    F = a^2+b^2+2*a*b+a+b+1;
    simplify(F)

[Clive Mingham]

this didn't work when I tried it in MuPAD

Answer 2

[Walter Roberson]

I do not know how you would best do this in MuPAD. In Maple, you would use the algsubs() routine, which MuPAD does not have.

You could try

simplify(subs(a^2+b^2+2*a*b+a+b+1, a, x-b))

Please note the difference between "ab" and "a*b" in a symbolic expression. a^2+b^2+2ab+a+b+1 is an algebraic expression but not a symbolic expression unless "2ab" is a variable name (which is possible to create in MuPAD, I believe.)