Scipy doesn’t produce multiple lines, the strange output is caused by the way you present your unsorted data to matplotlib. Sort your x-values and you get the desired output:
from scipy.optimize import curve_fit
from matplotlib import pyplot as plt
def func(x, a, b, c):
return a * x** b + c
# my data
pred_data = [3.0,1.0,1.0,7.0,6.0,1.0,7.0,4.0,9.0,3.0,5.0,5.0,2.0,6.0,8.0]
actu_data =[ 3.84,1.55,1.15,7.56,6.64,1.09,7.12,4.17,9.45,3.12,5.37,5.65,1.92,6.27,7.63]
popt, pcov = curve_fit(func, pred_data, actu_data)
#adjusting y
yaj = func(sorted(pred_data), *popt)
# plot the data
plt.plot(pred_data,actu_data, 'ro', label="Data")
plt.plot(sorted(pred_data),yaj,'b--', label="Best fit")
plt.legend()
plt.show()
A better way is of course to define an evenly-spaced high resolution array for your x-values and calculate the fit for this array to have a smoother representation of your fit function:
from scipy.optimize import curve_fit
import numpy as np
from matplotlib import pyplot as plt
def func(x, a, b, c):
return a * x** b + c
# my data
pred_data = [3.0,1.0,1.0,7.0,6.0,1.0,7.0,4.0,9.0,3.0,5.0,5.0,2.0,6.0,8.0]
actu_data =[ 3.84,1.55,1.15,7.56,6.64,1.09,7.12,4.17,9.45,3.12,5.37,5.65,1.92,6.27,7.63]
popt, pcov = curve_fit(func, pred_data, actu_data)
xaj = np.linspace(min(pred_data), max(pred_data), 1000)
yaj = func(xaj, *popt)
# plot the data
plt.plot(pred_data,actu_data, 'ro', label="Data")
plt.plot(xaj, yaj,'b--', label="Best fit")
plt.legend()
plt.show()