[Numpy-discussion] Inverse function of numpy.polyval()

[Neal Becker]

Yuxiang Wang wrote:

> Dear all,
> 
> I was wondering is there a convenient inverse function of
> np.polyval(), where I give the y value and it solves for x?
> 
> I know one way I could do this is:
> 
> import numpy as np
> 
> # Set up the question
> p = np.array([1, 1, -10])
> y = 100
> 
> # Solve
> p_temp = p
> p_temp[-1] -= y
> x = np.roots(p_temp)
> 
> However my guess is most would agree on that this code has low
> readability. Any suggestions?
> 
> Thanks!
> 
> -Shawn
> 
> 

Did you get the polynomial from polyfit?  In that case just swap x<->y