Fsolve function with values read from the workspace

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.

Answer 1

[Walter Roberson]

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);

[kamal kiki]

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)

Answer 2

[kamal kiki]

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.

Answer 3

[Victor Hugo Cantú]

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