MATLAB: Failure in initial objective function evaluation. FSOLVE cannot continue.

fsolve

I have looked over my code and can't find the problem. It has given me two errors, one when I was stepping through to try and find the issue:
"Unrecognized function or variable 'L' Error in MatlabHW_1 (line 46)" and when I ran it normally it gave me the fsolve error: "Error in fsolve (line 255)
fuser = feval(funfcn{3},x,varargin{:});"
I am not sure what this means and I haven't found any documentation on it, but for context here is my code:
function nacelle()
% *Constants:*
sigma = 5.67e-8;    %Stephan Boltzman constant
% *Variables:*
efficiency = 0.93;    %efficiency
A_gen = 4.2;          %[m^2] generator surface area
epsilon = 0.8;        %emissivity
T_inf = 30+273.15;    %[K] air temperature
power = 2.5e6;        %[W] generator power
                                
% *Set up array for temperature:*
h = linspace(30,80,10);         %array for increasing heat transfer coefficient
L = length(h);                  %find length of coefficient data
T = zeros(L,1);                 %set up temperature vector
%%
options=optimset('Display','off');   % Publishing purposes only Option to display output
for i=1:L
    T = fsolve(@(T) thefunct(T, epsilon, efficiency, T_inf, A_gen, power, sigma, h(i)), 300, options);
    T_s = T-273.15;             %convert to celsius
end
%% Plot and Results
plot(h,T_S)
xlabel('Heat Transfer coefficient [W/(m^2*K)]')
ylabel('Surface temperature [C]')
title('Wind Turbine Generator in Nacelle')
set(gca,'FontSize',14)
end
%% 
% *Residual function for finding temperature*
 function Res = thefunct(T, epsilon, efficiency, T_inf, A_gen, power, sigma, h)      
 
    Res = power - (h*A_gen*(T_S-T_inf)+sigma*A_gen*T_s^4+efficiency*power); 
 end

Best Answer

In thefunct() you confuse T and T_S and T_s
Also, the line
    T_s = T-273.15;             %convert to celsius

You need to save all of the values, such as
    T_S(i) = T-273.15;             %convert to celsius
Related Question