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 09:02 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. 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. I also have a couple of inequality constraints. Thanks in advance
From: Kittithad Wangveerathananon on 12 Aug 2010 10:16 Could somebody help me on this, please? It may sound absurd, but i've been trying to do this for, like, many hours.
From: Sean on 12 Aug 2010 10:30 "Kittithad Wangveerathananon" <kittithad(a)startfromyou.com> wrote in message <i40vno$9fm$1(a)fred.mathworks.com>... > Could somebody help me on this, please? > It may sound absurd, but i've been trying to do this for, like, many hours. Your question didn't get answered in an hour and 14 minutes. I think that's a very low response time for a bunch of people volunteering their time to help you. Also, please don't post the problem only in the thread title. What's wrong with this? >>solve('x^2+x+y^2+3*y=5*y^2+3*y+3*x*y+5','x')
From: Steven_Lord on 12 Aug 2010 10:46 "Kittithad Wangveerathananon" <kittithad(a)startfromyou.com> wrote in message news:i40rce$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
From: Kittithad Wangveerathananon on 12 Aug 2010 10:53
> What's wrong with this? > >>solve('x^2+x+y^2+3*y=5*y^2+3*y+3*x*y+5','x') Dear sean, it very nice of you for your respoonse. Sorry for the messing in the title. I'll keep that in mind. What I want is the set of (x*,y*) that solve the equation. Obviously, this problem is in the form of 2 variables and 1equation, so i should get an answer in form of set of (X,Y). 1) solve('x^2+x+y^2+3*y=5*y^2+3*y+3*x*y+5','x') gives me x in term of y. Then I need to create a vector yi to sub into x. I think the value of vector of y I created is not related to (x*,y*) that solve the equation. That's why xi=subs(x,y,yi) return a complex number. 2) solve('x^2+x+y^2+3*y=5*y^2+3*y+3*x*y+5','x','y') will, obviously, yield error message. Actually this is what i'm trying to do, the variable GBC is in the form of the equation in the title. %exo parameters tax=0.2; gamma=1; N0H=0.25; aH=1; nL=1; nH=3; d0=1; %endo parameters N0L=1-N0H; dH=d0*aH*nH; dL=2*dH; EzH=dH/2; EzL=dL/2; g=(nH-nL)/gamma; D=(1/dH)+(1/dL); disposible=1-tax; C=disposible*D; N1H=N0H; N1L=1-N1H; %Compute endo vars syms phi mew w=(1/(2*C))*(C*aH*nH-D*mew-(N1L/dL)*phi); e=(1/dH)*((1-tax)*w-mew); j=(1/dL)*((1-tax)*w-mew+phi); %number workers NLJ=j*N1L; NLU=(1-j)*N1L; NHE=e*N1H; NHU=(1-e)*N1H; %spending per workers SLJ=phi+g; SLU=mew; SHE=0; SHU=mew; %rev per workers RLJ=tax*w; RLU=0; RHE=tax*w; RHU=0; %firm's profitax from low FLJ=(aH*nH-w); FLU=0; FHE=(aH*nH-w); FHU=0; omega=NLJ*FLJ+NLU*FLU+NHE*FHE+NHU*FHU; %payoff of low PLJ=omega+w-EzL+phi; PLU=omega+mew; PHE=omega+w-EzH; PHU=omega+mew; %TS,TR and SWF TS=NLJ*SLJ+NLU*SLU+NHE*SHE+NHU*SHU; TR=NLJ*RLJ+NLU*RLU+NHE*RHE+NHU*RHU; GBC=TS-TR; swf=NLJ*PLJ+NLU*PLU+NHE*PHE+NHU*PHU; A=solve(GBC,mew); phii=0:0.02:2; mewi=subs(A,phi,phii); |