Find a good C factor

c_factor_min_evi.py

import numpy
import scipy.optimize

evi_vs_c = [
    (0.02874, 0.95),
    (0.18186, 0.25),
    (0.3643000126, 0.13575),
    (0.33039, 0.07075),
    (0.54826, 0.035425),
    (0.65346, 0.0001),
    ]

def c_factor(evi, a, b, c):
    return numpy.clip(
        1-a*numpy.exp(-evi**b)**c +
        0.07075 * (0.65346-evi)/(0.65346-0.33039),
        0.0001, 1.0)

p0, variant = scipy.optimize.curve_fit(
    c_factor,
    [x[0] for x in evi_vs_c],
    [x[1] for x in evi_vs_c],
    p0=[3, -0.3, 1],
    method='lm')

print(p0, variant)
for evi_val, expected in evi_vs_c:
    print(expected-c_factor(evi_val, *p0))