lsqcurvefit help - Field assignment to a non-structure array object

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Mar
Mar el 14 de En. de 2019
Comentada: Torsten el 16 de En. de 2019
Hi,
I am getting the error "Field assignment to a non-structure array object" in the line I call the lsqcurvefit function and I don't understand why.
I try to fit 2 different models. When I fit model_1 everything is fine. When I fit model_2 I got the error.
a, b - both vectors of size [1,41].
I have the following code:
opts = optimset('Display' ,'off');
for i=1:size(Image,1)
x(i,:) = lsqcurvefit (@model_1, init, a(1:end-1), Image(i, 1:end-1), zeros(size(init)), init*10, opts)
end
for i=1:size(Image,1)
x(i,:) = lsqcurvefit (@model_2, init, a(1:end-1), b(1:end-1), Image(i, 1:end-1), zeros(size(init)), init*10, opts)
end
Why do I get the error when I have one more entry in model_2? i.e. the vector b?
function y = model_2(p, a, b)
A = p(1);
B = p(2);
C = p(3);
D = p(4);
E = p(5);
y = A*exp(-a*C-b/D)+(1-A)*exp(-a*B).*(E*exp(-b/100)+(1-E)*exp(-b/40));
end
function y = model_1(p,a)
A = p(1);
B = p(2);
C = p(3);
y = A*exp(-B*a) + (1-A)*exp(-C*a);
end

Respuestas (1)

Walter Roberson
Walter Roberson el 14 de En. de 2019
Editada: Walter Roberson el 15 de En. de 2019
lsqcurvefit must have parameter order
  1. objective. @model_1 or @model_2
  2. x0. init in both cases
  3. xdata. a(1:end-1) in both cases
  4. ydata. Image(1:end-1) in the first case and b(1:end-1) in the second case
  5. lb. zeroes in the first case and Image(1:end-1) in the second case
  6. ub. init*10 in the first case and zeroes in the second case
  7. options. opt (a struct) in the first case and zeroes in the second case
  8. no documented parameter . absent in the first case and opt (a struct) in the second case.
Internally the code attempts to add additional fields to the struct expected in the 7th position and fails when the parameter is numeric zeroes .
  16 comentarios
Mar
Mar el 16 de En. de 2019
I evaluated it and It does return sensful values.
Torsten
Torsten el 16 de En. de 2019
Then you should do as "lsqcurvefit" suggests: Set a larger value for the maximum number of iterations:
options.MaxIterations and/or options.MaxFunctionEvaluations

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