How to apply custom equation on a curve and find unknown parameter

I've a curve and I've to apply following custom equation and have to find the unknown parameters A and B

y=3.379-(A*X^2/(B+X))

please guide me how can I do this operation.

Answer 1

[Andreas Goser]

When you write "I have a curve", I assume you have data. Make sure the data X and y is in your MATLAB workspace.

Start CFTOOL

Import the data (DATA button)

Use the FITTING button and choose customer equiation as TYPE OF FIT

[Andrew Newell]

If you have the Curve Fitting Toolbox.

[Andreas Goser]

True. Here an overview over multiple options with MATLAB: <http://www.mathworks.com/support/tech-notes/1500/1508.html>

But I'd say CFTOOL is the absolute easiest way for a new user to do fitting.

Answer 2

[Matt Tearle]

If you have Statistics Toolbox, use nlinfit.

f = @(b,x) 3.379 - (b(1)*x.^2./(b(2)+x))
bfit = nlinfit(xdata,ydata,f,b0)

where xdata and ydata are your data values to fit to, and b0 is an initial guess for the parameters

[Ketan Shende]

What does b0 look like?

[Walter Roberson]

In this b0 would be a vector of length 2 of numeric values, which will serve as initial guess for the search.