Fsolve function with values read from the workspace

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kamal kiki
kamal kiki el 11 de Feb. de 2012
Respondida: Victor Hugo Cantú el 25 de Mzo. de 2019
we all know that we use an m-file with the system of non-linear equations that we want to solve with Fsolve. I want the m-file that I have to use with Fsolve in order to solve the following system of non linear equations.
A.x^p1+2*y^2-5*x+7*y-40=0
3*x^2-y^2+4*x+B*y^p2-28=0
where x and y are the unknowns that must be given by the solution and A,B,p1 and p2 are values that must be read from the workspace.

Respuesta aceptada

Walter Roberson
Walter Roberson el 11 de Feb. de 2012
xy0 = [1,1]; %initial guess
eqn = @(xy) [A .* xy(1).^p1 + 2 .* xy(2).^2 - 5 .* xy(1) + 7 * y(2) - 40, 3 .* xy(1).^2 - xy(2).^2 + 4 .* xy(1) + B .* xy(2).^p2 - 28];
xy = fsolve(eqn, xy0);
  1 comentario
kamal kiki
kamal kiki el 12 de Feb. de 2012
xy0 = [1,1]; %initial guess
eqn = @(xy) [A .* xy(1).^p1 + 2 .* xy(2).^2 - 5 .* xy(1) + 7 * y(2) - 40, 3 .* xy(1).^2 - xy(2).^2 + 4 .* xy(1) + B .* xy(2).^p2 - 28];
xy = fsolve(eqn, xy0);
Thank you very much Walter roberson.
When an m-file exactly like this is saved and run it is working.but when I saved the m-file below:
function fcns=trial(z)
x=z(1);
y=z(2);
fcns(1)=A.*x.^p1+2.*y.^2-5.*x+7.*y-40;
fcns(2)=3.*x.^2-y.^2+4.*x+B.*y.^p2-28;
end
and when I entered in the command window:
A=1
B=2
p1=2
p2=1
guess=[2 3]
and after that I entered in the command window:
result=fsolve(@trial,guess)
I received the following error message:
??? Undefined function or variable 'A'.
Error in ==> trial at 4
fcns(1)=A.*x.^p1+2.*y.^2-5.*x+7.*y-40;
Error in ==> fsolve at 254
fuser = feval(funfcn{3},x,varargin{:});
Caused by:
Failure in initial user-supplied objective function evaluation. FSOLVE
cannot continue.
Please what is wrong in my m-file ? ( this same m-file is working when A,B,p1 and p2 are replaced by numbers in the m-file )
I am using m-files like this ones because working with x and y for me is easier than working with xy(1) and xy(2)

Iniciar sesión para comentar.

Más respuestas (2)

kamal kiki
kamal kiki el 12 de Feb. de 2012
xy0 = [1,1]; %initial guess eqn = @(xy) [A .* xy(1).^p1 + 2 .* xy(2).^2 - 5 .* xy(1) + 7 * y(2) - 40, 3 .* xy(1).^2 - xy(2).^2 + 4 .* xy(1) + B .* xy(2).^p2 - 28]; xy = fsolve(eqn, xy0);
Thank you very much Walter roberson.
When an m-file exactly like this is saved and run it is working.but when I saved the m-file below:
function fcns=trial(z)
x=z(1);
y=z(2);
fcns(1)=A.*x.^p1+2.*y.^2-5.*x+7.*y-40;
fcns(2)=3.*x.^2-y.^2+4.*x+B.*y.^p2-28;
end
and when I entered in the command window:
A=1
B=2
p1=2
p2=1
guess=[2 3]
and after that I entered in the command window:
result=fsolve(@trial,guess)
I received the following error message:
??? Undefined function or variable 'A'.
Error in ==> trial at 4
fcns(1)=A.*x.^p1+2.*y.^2-5.*x+7.*y-40;
Error in ==> fsolve at 254
fuser = feval(funfcn{3},x,varargin{:});
Caused by:
Failure in initial user-supplied objective function evaluation.
FSOLVE
cannot continue.
Please what is wrong in my m-file ? ( the same m-file is working when A,B,p1 and p2 are replaced by numbers in the m-file )
I am using m-files like this one because working with x and y for me is easier than working with xy(1) and xy(2)
Also the m-file must have a name because I need it to use it when I am entering the f-solve command in the command window.

Victor Hugo Cantú
Victor Hugo Cantú el 25 de Mzo. de 2019
A = 1; B = 2; p1 = 2; p2 = 1;
guess = [2 3];
% x(1) = x; x(2) = y;
x = fsolve(@(x) trial(x,A,B,p1,p2), guess)
function F = trial(x,A,B,p1,p2)
F(1) = A*x(1)^p1 + 2*x(2)^2 - 5*x(1) + 7*x(2) - 40;
F(2) = 3*x(1)^2 - x(2)^2 + 4*x(1) + B*x(2)^p2 - 28;
end

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