Attempting to fit data with a sigmoid curve, but not an option in curvefitter toolbox

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Levi Matsushima
Levi Matsushima 2024-8-21
回答： Image Analyst 2024-8-21
I am working on fitting data with a sigmoidal curve, but my CurveFitter toolbox does not have the sigmoidal option under fit types. I have tried a custom fit, but it is not giving me any useable fits.
eqn:
'a/(1+exp(-b*(x-c)))'

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回答（3 个）

Star Strider
Star Strider 2024-8-21
Ran in:
Perhaps something like this —
s = fittype('a/(1+exp(-b*(x-c)))', 'Coefficients',{'a','b','c'}, 'Independent','x', 'Dependent','y')
s =
General model: s(a,b,c,x) = a/(1+exp(-b*(x-c)))
x = linspace(0, 10, 20);
y = rand(size(x));
sfit = fit(x(:), y(:), s)
Warning: Start point not provided, choosing random start point.
sfit =
General model: sfit(x) = a/(1+exp(-b*(x-c))) Coefficients (with 95% confidence bounds): a = 58.84 (-1.583e+05, 1.584e+05) b = 0.05918 (-1.317, 1.435) c = 85.92 (-4.764e+04, 4.781e+04)
figure
plot(sfit, x, y)
grid
.
Sam Chak
Sam Chak 2024-8-21
Ran in:
Hi @Levi Matsushima
The latest Curve Fitting Toolbox has only three Sigmoidal Curves in its library of models.
rng(0,"twister")
x = linspace(-1, 1, 101)';
y = 1./(1 + exp(- 10*x)) + 0.02*randn(101, 1);
y(y>1) = 1;
y(y<0) = 0;
logsigm = fit(x, y, 'logistic')
logsigm =
General model Logistic: logsigm(x) = a/(1 + exp(-b*(x-c))) Coefficients (with 95% confidence bounds): a = 0.9933 (0.9863, 1) b = 10.2 (9.769, 10.63) c = -0.001955 (-0.006753, 0.002844)
plot(logsigm, x, y), grid on, grid minor
Image Analyst
Image Analyst 2024-8-21
Attach your actual data so we can work with it. In the meantime, I'm attaching my demo of fitting a sigmoid, though it uses a different formula than yours. However, you can adapt it to use your formula.

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