Title: argmin and argmax
Slug: argmin_and_argmax
Summary: An explanation of argmin and argmax in Python.
Date: 2016-01-23 12:00
Category: Mathematics
Tags: Basics
Authors: Chris Albon

argmin and argmax are the inputs, x's, to a function, f, that creates the smallest and largest outputs, f(x).

Preliminaries



In [1]:

    
import numpy as np
import pandas as pd
np.random.seed(1)

Define A Function, f(x)



In [2]:

    
# Define a function that,
def f(x):
    # Outputs x multiplied by a random number drawn from a normal distribution
    return x * np.random.normal(size=1)[0]

Create Some Values Of x



In [3]:

    
# Create some values of x
xs = [1,2,3,4,5,6]

Find The Argmin Of f(x)



In [4]:

    
#Define argmin that
def argmin(f, xs):
    # Applies f on all the x's
    data = [f(x) for x in xs]

    # Finds index of the smallest output of f(x)
    index_of_min = data.index(min(data))
        
    # Returns the x that produced that output
    return xs[index_of_min]



In [5]:

    
# Run the argmin function
argmin(f, xs)









    Out[5]:





6

Check Our Results



In [6]:

    
print('x','|', 'f(x)')
print('--------------')
for x in xs:
    print(x,'|', f(x))









    



x | f(x)
--------------
1 | 1.74481176422
2 | -1.52241380179
3 | 0.957117288171
4 | -0.99748150191
5 | 7.31053968522
6 | -12.360844257