inv_transform.py

import numpy as np
def inv_yeojohnson(y, lmbda):
    if lmbda == 0:
        # Lambda = 0
        return np.where(y >= 0, np.exp(y) - 1, 1 - np.exp(-y))
    else:
        # Lambda != 0
        pos_part = np.where(y >= 0, (y * lmbda + 1) ** (1 / lmbda) - 1, 0)
        neg_part = np.where(y < 0, 1 - (-(2 - lmbda) * y + 1) ** (1 / (2 - lmbda)), 0)
        return pos_part + neg_part