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

Mar

2019 1 14

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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

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回答（1 个）

Walter Roberson 2019-1-14

编辑：Walter Roberson 2019-1-15

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lsqcurvefit must have parameter order

objective. @model_1 or @model_2
x0. init in both cases
xdata. a(1:end-1) in both cases
ydata. Image(1:end-1) in the first case and b(1:end-1) in the second case
lb. zeroes in the first case and Image(1:end-1) in the second case
ub. init*10 in the first case and zeroes in the second case
options. opt (a struct) in the first case and zeroes in the second case
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 .