How can I use isqurvefit or fminsearch to have my coefficient of the function?

Hi everyone,

I have the following function, how can I get the value of A,B and n by curve fitting, I tried but I was not successful.

Initial guesses for:

A=0.0005; B=0.14; n=2

y=[7.754e-05 6.825e-05 6.2156e-05 5.9374e-05 5.803e-05 5.3958e-05 5.1747e-05 4.9142e-05 8.2671e-05 7.7143e-05];
x=[0.592 0.652 0.693 0.726 0.751 0.772 0.790 0.820 0.452 0.525];
y=A+B*(x)^n;

Thanks in advance

[Matt J]

Does n have to be an integer?

Answer 1

[Star Strider]

This works with lsqcurvefit:

y=[7.754e-05 6.825e-05 6.2156e-05 5.9374e-05 5.803e-05 5.3958e-05 5.1747e-05 4.9142e-05 8.2671e-05 7.7143e-05];
x=[0.592 0.652 0.693 0.726 0.751 0.772 0.790 0.820 0.452 0.525];

[x,ix] = sort(x);
y = y(ix);

% MAPPING: b(1) = A,  b(2) = B,  b(3) = n
f = @(b,x) b(1) + b(2).*x.^b(3);

B0 = [5E-4, 0.14, 2];
Prms = lsqcurvefit(f, B0, x, y);

figure(1)
plot(x, y, 'bp')
hold on
plot(x, f(Prms,x), '-r')
hold off
grid