Hi Zoltán,
I only need sqrt, so probably I will... use... just the simple Newton alg.
It is still not clear to me what type you want to work in. Is it Rational? In that case, you don't need the Newton algorithm. realToFrac . sqrt . realToFrac works fine, as you originally suggested. If that gives too much precision, you can use (`approxRational` epsilon) . sqrt . realToFrac Newton will not work in general for Fractional. It works for Floating, but there you already have the sqrt function. Are you using a type that has a Fractional instance, does not have a Floating instance, and Newton works and is needed? What type is that?
a good math library would make Matlab obsolete. :)
Yes, that would certainly be nice. This has been discussed at length several times on this list in the past. I wonder if there has been any further progress on it. Regards, Yitz