MATLAB: How to fix the upper asymptote in sigmoid

curve fittingsigmoid

Hello, I have a sigmoid equation. My qestion is in a comment here:
https://www.mathworks.com/matlabcentral/answers/505984-fitting-a-sigmoid-curve-using-curve-fitting-tool-box
The problem I am facing is, this sigmoid equation is a power curve and needs to reach a certain fixed height at the rated speed (variable 'a'). But I am not able to adjust my upper assymptode anything above 650, even by forcing my a to be an independent variable and also by replacing a by 900. Since, I am new to sigmoid, I would like some help to rewrite this piece of code to make my sigmoid reach 'a'. Also, I def need my xon, xoff and the everything about the curve from below to remain the same.
TIA 
xon =3;
xrated = 12.5;
off=25;
a=900;
ft = fittype(@(b,c,x) mysigmoid(b,c,x,xon,xrated,a));
mdl = fit(x',y',ft,'start',[5 20]);
function yhat= mysigmoid(b,c,xon,xrated,a)
x= max(xon,min(x,xrated))
yhat = a./(1+exp(-(x-c)/b))- a./(1+exp(-(xon-c)/b));
end

Best Answer

Your call to mysigmoid has 6 input arguments (b,c,x,xon,xrated,a; the last of which is your "a"), but your defined function only accepts 5 (b,c,xon,xrated,a). you're missing the 'x' input argument in your function definition.
This is likely leading to your issues with manually setting the "height" of the sigmoid function.
Related Question