MATLAB: FSOLVE requires all values returned by functions to be of data type double.

fsolve errorMATLAB and Simulink Student Suitenonlinear equationssystem

I don't know how to solve this problem

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The solution is straightforward. Be sure your ‘roottwod’ function returns double-precision values. Note that symbolic values are not double-precision values.

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MATLAB: Minimize a function to a desired value

"D to be minimised to a certain value" -- so you don't actually want to minimize your function but instead want to find a solution to the system of equations fun(x) = certain_value [or to write it another way, fun(x) - certain_value = 0? In that case, take a look at fsolve instead of lsqnonlin.

MATLAB: FSOLVE requires all values returned by functions to be of data type double.

Call the function with one parameter vector:

fcn = @(b) F(b(1),b(2),b(3));

and with that change, this works:

L0 = 3;                                                                         % Create Value






V0 = 5;                                                                         % Create Value
SP0 = 7;                                                                        % Create Value
tet = rand;                                                                     % Create Value
bet = rand;                                                                     % Create Value
tau = rand;                                                                     % Create Value
chi = rand;                                                                     % Create Value
x0=[L0; V0; SP0];
F=@(L, V, SP) [L-V/(tet-bet*(V*SP)); 1-chi*(SP*L+(1/bet))+tau*L; V-chi+(1-chi)*bet*V*(SP*L+(1/bet))];
options = optimset ('Display', 'Final', 'Tolx', 1e-10,'Tolfun',1e-10);
fcn = @(b) F(b(1),b(2),b(3));
B = fsolve(fcn, x0, options)

Supply the correct scalar values to get the intended result.

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MATLAB: Minimize a function to a desired value

MATLAB: FSOLVE requires all values returned by functions to be of data type double.

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