使用lmfit未定义参数

Question

I am trying to fit a curve to the equation below with the given data. The equation is Rate=k*Concentration^n . I am having trouble as the n when fitted is -6 , which is not possible so I am trying to set a bound at min=0 . However, I am getting a undefined term parameter errors. Any help would be great thanks.

from IPython import get_ipython 
get_ipython().magic('reset -sf')
import numpy as np
from lmfit import Model
import matplotlib.pyplot as plt



# Homework Problem #2 
Time = np.array ([0, 48, 76, 124, 204, 238, 289])
Concentration =np.array ([19.04, 17.6, 16.9, 15.8, 14.41, 13.94, 13.37])

# Rate Determination 
Rate=Concentration/Time 


# Model Definition 

def rateEq(Concentration, k, n):
    return k*(Concentration)**n

# Model creation
model=Model(rateEq)

# Parameters
params = parameters()
params.add(k=0.001)
params.add(n=0.001)
par.set(min=0)


# Data Fit v
result=model.fit(Rate, params, Concentration=Concentration)
# Print and Plot Results 
print(result.fit_report())
result.plot_fit()

Answer 1

parameters is undefined because you do not define it anywhere. You use it as params = parameters() , probably implying a function call, but you do not define or import that function.... Similarly, par is undefined because you do not define it anywhere.

You almost certainly want

from lmfit import Model, Parameters # explicitly import Parameters

params = Parameters() # note the capitalization
params.add('k', value=0.001)
params.add('n', value=0.001)

what is less clear (because I cannot guess what par is) is whether you want

params['k'].min = 0

or

params['n'].min = 0

Also, just as a warning: Since your time[0] is 0, your Rate[0] will be infinite, which will cause trouble when running the fit.