suppose I have an equation x^2+x+y^2+3*y=5*y^2+3*y+3*x*y+5 and I want to find the set of (x,y) that satisfy the equation.
in [Matlab]
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From: Kittithad Wangveerathananon on 12 Aug 2010 11:06 Yeah basically, that what I want. But I need to obtain the value of those pairs, because I want to use it to sub into my objective function to find that which pair max my objective. I used fmincon before, but feel that the answer is not quite right, since I'm not familiar with the function. So I decided to go manually. "Steven_Lord" <slord(a)mathworks.com> wrote in message <i411fm$4e0$1(a)fred.mathworks.com>... > > > "Kittithad Wangveerathananon" <kittithad(a)startfromyou.com> wrote in message > news:i40rce$qur$1(a)fred.mathworks.com... > > Question > > How can i do that? > > I've been trying, solve, explot and subs. > > I can get the graph, but i cannot get the (x,y) pairs that I want. > > What, specifically, do you want to obtain? There are an infinite number of > (x, y) points that satisfy this equation. One such pair is approximately > (3, -2.8615). > > > When I use function solve to solve the equation in term of x or y and then > > substitute the numeric value for one of them to find the other, I got the > > problem about complex numer. This might be because that numeric value that > > I substitute is not the number that satisfy the equation, so the program > > give me the result in complex number. > > > > Background. > > I need to use the pairs to find the optimal value of my objective > > function. > > I tried to use the fmincon, but it gave me the optimal value that is not > > reliable, so i try to do it manually. > > Note that my equality constraint is in the form of the equation in the > > subject. > > Don't do that. Please put your ENTIRE question in the body of your message, > for easy quoting. > > > I also have a couple of inequality constraints. > > If you were just looking to identify the points that satisfy your equation > graphically, I would use CONTOUR. Write your equation as z = f(x, y) and > look at the contour for z = 0. > > -- > Steve Lord > slord(a)mathworks.com > comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ > To contact Technical Support use the Contact Us link on > http://www.mathworks.com |