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

fsolvfunction

Hi,
I have defined a simple function, to solve numerically a system of 3 equeations, 3 unknows, but I keep receiving this error:
FSOLVE requires all values returned by functions to be of data type double.
Shoul I use another solver due to myt equations?
here is the code
function [L, V, SP]=steadystate_helper(L0, V0, SP0, bet, tet, chi, tau)
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);
[L, V, SP]=fsolve(@(L, V, SP) F, x0, options);

Best Answer

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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