Add argument in scipy.optimize

Question

I am trying to use scipy.optimize.minimize (simplex method) for minimizing the following function

argmin (sum(i=0 to 9) (a*i - b_i)**2)

I would like to obtain the value of a. I have 10 values of b_i (i have it already calculated outside the function) that i want to insert in the function

def f(a, b):
    func = 0
    for i in range(10):
        func+= (a*i - b[i])**2
    return func
init = [1]
out= optimize.minimize(f, init, method='nelder-mead')

it gives an error saying: f() missing 1 required positional argument: 'b'

How can i make it run.

What if you do init = [1 , 1]? You should pass two values to objective function. Or def f(a) (as you said b calculated already, then just remove it from arguments.) — Shayan
– Shayan, Commented Feb 15, 2022 at 16:12
but b is not one value, it has 10 values. I have corrected now. — Lalu
– Lalu, Commented Feb 15, 2022 at 16:15
Great! Put b[i] instead of b! I mean : func+= (a*i - b[i])**2 and also remove b from function arguments. — Shayan
– Shayan, Commented Feb 15, 2022 at 16:17

Shayan · Accepted Answer · 2022-02-15 16:19:38Z

2

what about this:

def f(a):
    func = 0
    for i in range(10):
        func+= (a*i - b[i])**2
    return func
init = [1]
out= optimize.minimize(f, init, method='nelder-mead')

as you said your target variable is a and you have values for b, then you need to construct Obj function with one argument I guess.

answered Feb 15, 2022 at 16:19

Shayan

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2 Comments

Lalu Over a year ago

where do i define b[i]? outside the function?

Shayan Over a year ago

@Lalu Exactly before the function, you should define b! it should be something iterable like a list. for example: b = [1,2,3] (values maybe something else I don't know what they are.)

Muhammad Mohsin Khan · Accepted Answer · 2022-02-16 11:04:55Z

0

There is an optional parameter called args() in scipy.optimize.minimize using which you can pass arguments to the objective function as a tuple. You can do this as follows:

from scipy.optimize import minimize
b = [1,2,3,4,5,6,7,8,9,10] # for example

def f(a, b):
    func = 0
    for i in range(10):
        func+= (a*i - b[i])**2
    return func

init = [1]
out = minimize(f, init, args=(b), method='nelder-mead')
print(out)

answered Feb 16, 2022 at 11:04

Muhammad Mohsin Khan

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