What is the plot of following function

133 Views Asked by At

What would the plot for $ x^{x^{x^{x^x...}}}$ look like for $x \in\mathbb{R}$?

I think all math-tools try to compute it recursively which end up with the error "standard computation time exceeded".

And sory, I could not express it well in the title.

2

There are 2 best solutions below

3
On BEST ANSWER

It looks something like this: Knuthpower

where the even powers converge to the blue line and the odd powers converge to the yellow line. The point where these two converges to the same value is near $0.07$.

As pointed out in the comments, this function is not defined outside $[0,1]$ since the sequence $(x \uparrow\uparrow n)_{n=0}^\infty$ escapes to infinity.

Edit: This function also converges in $[1,e^{1/e}]$ according to StackTD's answer.

1
On

The infinite power tower $$x^{x^{x^{x^x{^{^{\cdot^{\cdot^{\cdot}}}}}}}}$$ converges only for $e^{-e} \le x \le e^{1/e}$, which is approximately in the interval $[0.0659 \,,\, 1.4446]$.

In that interval, the power tower can be rewritten in terms of the Lambert W-function which you can then use to have the graph plotted by computer software:

$$x^{x^{x^{x^x{^{^{\cdot^{\cdot^{\cdot}}}}}}}} = -\frac{W\left( -\ln x \right)}{\ln x}$$

enter image description here

You can also take a look at this plot by WolframAlpha.