Restricting values for curve_fit (scipy.optimize)

Question

I\'m trying to fit a logistic growth curve to my data using curve_fit using the following function as the input.

def logistic(x, y0, k, d, a, b):
    if b > 0         


        

Answer 1

When the parameters fall out of the admissible range, return a wildly huge number (far from the data to be fitted). This will (hopefully) penalize this choice of parameters so much that curve_fit will settle on some other admissible set of parameters as optimal:

def logistic(x, y0, k, d, a, b):
    if b > 0 and a > 0:
        y = (k * pow(1 + np.exp(d - (a * b * x) ), (-1/b) )) + y0
    elif b >= -1 or b < 0 or a < 0:
        y = (k * pow(1 - np.exp(d - (a * b * x) ), (-1/b) )) + y0
    else:
        y = 1e10
    return y