How to fix the upper asymptote in sigmoid?

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

Answer 1

[Shae Morgan]

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.

[Srilatha Raghavan]

Sorry that's a typo. My function does have 6 input arguments. Another thing I noticed is, when my height (the value of 'a') is smaller ( From 90-450), the height of the sigmoid does follow the value I am assigning it to.

I have attached my code as well. Thank you

[Shae Morgan]

your attached code doesn't run without the data "windspeed' and "tgeneration" could you provide some sample data for that?

[Shae Morgan]

your code still doesn't run after reading in these X and Y values. Please provide a code that will run so it can be used.

ex. missing 'b', 'c', and 'x' values.

[Srilatha Raghavan]

I figured this out! If the data that is used to initialize the fit does not reach the required upper symptote, we cannot expect the model to do what want it to with our data. It was a basic understanding of the sigmoid and curve fitting toolbox. Anyways thank you.