Error: Custom function fitting in MATLAB

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LM
LM 2023-4-18
评论： Cris LaPierre 2023-4-19
Ran in:
Hey guys, I would like to know why I got this error and how can I fix it. Can I please have your guys comments on this code:
% Load the experimental data and assgin the data to each parameter
data2fit2 = xlsread('data2fit2.xlsx');
ST = data2fit2(:,1);
theta_bar = data2fit2(:,2);
f_exp = data2fit2(:,3);
% Initial Guess
par0 = [0.417257,0.04132,0.001177,0.00961,1.946234];
pars = zeros(size(par0));
% Get the estimate parameters to have best fit to measurement data
par = fminsearch(@(par) err_fcn(pars,...
data2fit2,...
ones(size(data2fit2)),...
@(s,t,p) epsilon_f_of_sigma(s,t,p),...
ST,...
theta_bar),...
par0);
Arrays have incompatible sizes for this operation.

Error in solution>err_fcn (line 63)
err = sum((data2fit2(:) - model_data(:)).^2.*weights4scaling);

Error in solution>@(par)err_fcn(pars,data2fit2,ones(size(data2fit2)),@(s,t,p)epsilon_f_of_sigma(s,t,p),ST,theta_bar) (line 12)
par = fminsearch(@(par) err_fcn(pars,...

Error in fminsearch (line 216)
fv(:,1) = funfcn(x,varargin{:});
% Use optimized parameters to calculate the estimated epsilon_f by HC model
epsilon_f_modeled = epsilon_f_of_sigma(ST, theta_bar, par);
% Plot fracture criterion
figure;
plot(ST, f_exp, 'o', ST, epsilon_f_modeled, '-')
xlabel('Stress Triaxiality [-]')
% ylabel('Lode Angle Parameter [-]')
ylabel('Equivalent Plastic Strain at Fracture [-]')
function epsilon_f = epsilon_f_of_sigma(ST, theta_bar, pars)
b0 = pars(1);
gamma = pars(2);
c = pars(3);
epsilon_p = 0.0005;
epsilon_0 = 0.0005;
n = pars(4);
a = pars(5);
% Determine strain rate effect on parameter b
if epsilon_p < epsilon_0
b = b0;
else
b = b0*(1 +gamma*log(epsilon_p/epsilon_0));
end
% Define Lode-dependent functions
f1 = (2/3)*cos((pi/6)*(1-theta_bar));
f2 = (2/3)*cos((pi/6)*(3+theta_bar));
f3 = -(2/3)*cos((pi/6)*(1+theta_bar));
% Define each term
Strain_rate_term = b*(1+c).^(1./n);
Lode_dependent_term = ((1/2).*((f1-f2).^a+(f2-f3).^a+(f1-f3).^a)).^(1./a);
Triaxiality_term = c.*(2*ST+f1+f3);
% Final expression for HC model
epsilon_f = Strain_rate_term.* (Lode_dependent_term + Triaxiality_term).^(-1./n);
end
% Define error function
function err = err_fcn(pars,data2fit2,weights4scaling,model_fcn,ST,theta_bar)
model_data = model_fcn(ST,theta_bar,pars);
err = sum((data2fit2(:) - model_data(:)).^2.*weights4scaling);
end

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采纳的回答

Cris LaPierre
Cris LaPierre 2023-4-18
Ran in:
data2fit2(:) and model_data(:) and weights4scaling do not all have the same size.
A = rand(3)
A = 3×3
0.6170 0.3529 0.7404 0.5912 0.8156 0.0387 0.5109 0.5150 0.8625
B = rand(2,1)
B = 2×1
0.7242 0.0795
% Your error
A-B
Arrays have incompatible sizes for this operation.
  4 个评论
显示 2更早的评论
LM
LM 2023-4-19
Hi Cris, I literally confused right now. Would you mind to give me some tips on this?
- For you mentioned equation, which is for caculating the damage parameter and I think it will not be involved in the fitting equation.
And yes, I agree with you guys on fitting on the measurement data, and I just don't know which step I made wrong. My apologies to this.
Cris LaPierre
Cris LaPierre 2023-4-19
No, the new equation does not play a role in obtaining the fit parameters.
Perhaps you are trying to do too much at once. Simplify your code down to just fitting the equation to your data. Get rid of all your extra variables and unnecessary arrays of ones.

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