Thanks, I see it, but if I create a derivatrion "diff" the sign is important: If I run formula.diff(a, 1): [0.5*(t-ax^3)^2]' => -(t-a*x^3)*x^3 [0.5*(ax^3-t)^2]' => (a*x^3-t)*x^3 On my code I parse the formula (0.5)*(t -(formula)^2 and substitute formula with another formula. I do not understand why the minus sign is not interpreted correctly. I think GiNaC does create a pattern matching and not evaluate the correct expression. In my opinion the first expression is the correct one, GiNaC creates the second. Why? How can I tell GiNaC that it interpret the expression arithmetically correct? Thanks Phil Am 06.08.2010 um 22:41 schrieb Doug:
(-1)^2 == 1^2 therefore (-expr)^2 == expr^2 therefore (t-exp(x))^2 == (-(t-exp(x))^2 == (exp(x) - t)^2
Do you see it now?
I'm now a little bit confused, cause I'm working for a long time with this problem and I don't see my "thinking error". If I have an expression eg exp(x), so (t-exp(x))^2 is not the same (exp(x)-t)^2. Sorry I don't see it
Thanks
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