## sigm_fit

Version 1.5.0.0 (4.11 KB) by
Optimization of parameters of the sigmoid function
Updated 30 Mar 2016

Optimization of parameters of the sigmoid function

Syntax:
[param]=sigm_fit(x,y)

that is the same that
[param]=sigm_fit(x,y,[],[],[]) % no fixed_params, automatic initial_params

[param]=sigm_fit(x,y,fixed_params) % automatic initial_params
[param]=sigm_fit(x,y,[],initial_params) % use it when the estimation is poor
[param]=sigm_fit(x,y,fixed_params,initial_params,plot_flag)

param = [min, max, x50, slope]

if fixed_params=[NaN, NaN , NaN , NaN] % or fixed_params=[]
optimization of "min", "max", "x50" and "slope" (default)

if fixed_params=[0, 1 , NaN , NaN]
optimization of x50 and slope of a sigmoid of ranging from 0 to 1

Additional information in the second output, STAT
[param,stat]=sigm_fit(x,y,fixed_params,initial_params,plot_flag)

Example:
%% generate data vectors (x and y)
fsigm = @(param,xval) param(1)+(param(2)-param(1))./(1+10.^((param(3)-xval)*param(4)))
param=[0 1 5 1]; % "min", "max", "x50", "slope"
x=0:0.1:10;
y=fsigm(param,x) + 0.1*randn(size(x));

%% standard parameter estimation
[estimated_params]=sigm_fit(x,y)

%% parameter estimation with forced 0.5 fixed min
[estimated_params]=sigm_fit(x,y,[0.5 NaN NaN NaN])

%% parameter estimation without plotting
[estimated_params]=sigm_fit(x,y,[],[],0)

### Cite As

R P (2024). sigm_fit (https://www.mathworks.com/matlabcentral/fileexchange/42641-sigm_fit), MATLAB Central File Exchange. Retrieved .

##### MATLAB Release Compatibility
Created with R13
Compatible with any release
##### Platform Compatibility
Windows macOS Linux
##### Categories
Find more on Curve Fitting Toolbox in Help Center and MATLAB Answers
##### Acknowledgements

Inspired by: Sine function fit

Inspired: sigmoid, sigm_fit_val(param,x)

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Version Published Release Notes
1.5.0.0

plot bug fixed
title update

1.4.0.0

minmax function used in plotting substituted by min and max functions

1.3.0.0

STAT output variable, with confidence intervals for parameters and distribution

1.0.0.0