Issue with PH model median method

[benoitdes]

Hello,

I found an error when using the Proporitionnal Hazard Model. When I try to compute the median, I got an error (while it works with the mean). According to the documentation, both methods should accept similar arguments.

See the following code snippet to reproduce the error

import numpy as np
from relife.models import Weibull, ProportionalHazard
 
model = ProportionalHazard(Weibull(7, 0.05), coef=(0.1, 0.2))
covar = np.random.random((10,2))
 
model.mean(covar[3, :]) # OK
model.median(covar[3, :]) # ERROR