On Tuesday, 20 September 2016 at 16:22:19 UTC, H. S. Teoh wrote:

On Tue, Sep 20, 2016 at 12:35:18PM +0000, Basile B. viaDigitalmars-d-learn wrote: [...]The problem is here: https://github.com/BBasile/iz/blob/master/import/iz/math.d#L849 - f(x,c) = 1.0 - pow(1.0 - pow(x, 2.0/c), c * 0.5); - c(f0.5)) = ?## Advertising

Which means that I ask you if you can isolate c for y = 1.0 - pow(1.0 - pow(0.5, 2.0/c), c * 0.5); y is always f(0.5,c)I couldn't manage to solve it. Nested exponentials are verynasty to invert. :-( At first, I thought it might be solvablein terms of the Lambert W function (aka ProductLog) but Icouldn't manage to get the equation into the right form. ThenI checked on Wolfram Alpha and it says "no result found interms of standard mathematical functions".That probably means the inverse cannot be expressed in terms ofelementary functions. Probably the only thing you can do is touse some kind of numerical approximation, like some form ofNewton's method or some such, to find the value of c.T

`Thanks for trying, you're not the first to tell me about the`

`Newton's method...`