first I have to apologize for any uncorrect naming or categorisation of my question, as I am an electrical engineer rather than a mathematican.
I try to find a simple solution for my problem:
I have a given number of data points (x,y) that "look like" they could be approximated by an easy function. As this will be used in a simulation many times, calculation time quite matters and therefore I can't implement it as a lookup table. Also, some error isn't a problem at all.
There are some online tools, that do what I want:
Nevertheless, my data looks pretty much like -sqrt(x). So do you now any tools that includes regressions by (square?) roots? Because a sqrt() function isn't approximated very well by polynomial equations for values near the x axis.
Thank you very much!
Edit: It rather looks like sqrt(-x), I added an image.