How to compare values of mathematic functions in a python function (def)

Question

I am writting a code to compare mathematic functions and say which one of them has the biggest value for given x and y

import math

def r(x,y):
  r = 3 * math.pow(x, 2) + math.pow(y, 2)
  return r

def b(x,y):
  b = 2 * math.pow(x, 2) + 5 * math.pow(y, 2)
  return b

def c(x,y):
  c = -100 * x + math.pow(y, 3)
  return c

def compare():
  x = float(input("Type the value of x: "))
  y = float(input("Type the value of y: "))
  r(x,y)
  b(x,y)
  c(x,y)

  if r > b and c:
    print("r is the biggest.")
    return
  elif b > r and c:
    print("b is the biggest.")
    return
  elif c > b and r:
    print("c is the biggest.")
    return

compare()

But I get the following error:

TypeError: '>' not supported between instances of 'function' and 'function'

IoaTzimas · Accepted Answer · 2020-10-29 17:42:29Z

1

You must assign the result of each function to a variable. Try the following:

import math

def r(x,y):
  r = 3 * math.pow(x, 2) + math.pow(y, 2)
  return r

def b(x,y):
  b = 2 * math.pow(x, 2) + 5 * math.pow(y, 2)
  return b

def c(x,y):
  c = -100 * x + math.pow(y, 3)
  return c

def compare():
  x = float(input("Type the value of x: "))
  y = float(input("Type the value of y: "))
  R=r(x,y)
  B=b(x,y)
  C=c(x,y)

  if R > B and R>C:
    print("r is the biggest.")
    return
  elif B > R and B>C:
    print("b is the biggest.")
    return
  elif C > B and C>R:
    print("c is the biggest.")
    return

compare()

edited Oct 29, 2020 at 17:42

answered Oct 29, 2020 at 17:26

IoaTzimas

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1 Comment

Samwise Over a year ago

Your code carries over a bug from OP involving comparisons and and. ;)

Samwise · Accepted Answer · 2020-10-29 17:57:12Z

There are two bugs here:

You need to compare the actual results of the function, not the function object itself.
You can't compare one numerical value to the and of two other values; what you're actually testing for in that case is a single comparison plus whether the other value is non-zero!

I'd use the max function to get the largest value rather than building a complicated chain of conditionals to do the same thing. That way if you add another function it's easy to just add it to the list:

import math

def r(x, y):
    return 3 * math.pow(x, 2) + math.pow(y, 2)

def b(x, y):
    return 2 * math.pow(x, 2) + 5 * math.pow(y, 2)

def c(x, y):
    return -100 * x + math.pow(y, 3)

def compare():
    functions = [r, b, c]  # maybe this could be a parameter?
    x = float(input("Type the value of x: "))
    y = float(input("Type the value of y: "))

    result, func_name = max((f(x, y), f.__name__) for f in functions)
    print(f"{func_name} is the biggest.")

compare()

Type the value of x: 1
Type the value of y: 2
b is the biggest.

Type the value of x: 0
Type the value of y: 0
r is the biggest.

Type the value of x: -1
Type the value of y: -2
c is the biggest.

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