Topic: getting coefficients

I am not a mathematician, but I use Graph for some of my engineering work. I have an equation:
         f(x) = a {sin[atan(-bx]}
and a set of points. I determined a and b by trial and error to make the curve match the points. Is there a better method to let the software do the work?

Re: getting coefficients

Yes, Graph can help you with that.

1. First you create a point series with your data points.
2. Select the point series and choose Function|Insert trendline in the menu.
3. In the User defined tab, you can specify your model as $a*sin(atan(-$b*x))
4. You can optionally use the Add model button to store the model for later use. It also allows you to change the default guess, which is sometimes needed.
5. When you click the OK button, Graph will create a function from your model that fits your point series.

Re: getting coefficients

Thanks! I will try this. I am citing your program in a magazine article about measuring satellite velocity and distance.