lagrange-multipliers.py

# salimt
# Import libraries
# Import libraries
import numpy as np
from scipy import optimize

# First we define the functions, YOU SHOULD IMPLEMENT THESE
def f (x, y) :
  return - np.exp(x - y**2 + x*y)

def g (x, y) :
  return np.cosh(y) + x - 2

def dfdx (x, y) :
  return (1 + y) * f (x, y)

def dfdy (x, y) :
  return (- 2*y + x) * f (x, y)

def dgdx (x, y) :
  return 1

def dgdy (x, y) :
  return np.sinh(y)

# Use the definition of DL from previously.
def DL (xyλ) :
    [x, y, λ] = xyλ
    return np.array([
            dfdx(x, y) - λ * dgdx(x, y),
            dfdy(x, y) - λ * dgdy(x, y),
            - g(x, y)
        ])

# To score on this question, the code above should set
# the variables x, y, λ, to the values which solve the
# Langrange multiplier problem.

# I.e. use the optimize.root method, as you did previously.

x, y, λ = (1,0,1)
x, y, λ = optimize.root(DL, [x, y, λ]).x
print("x = %g" % x)
print("y = %g" % y)
print("λ = %g" % λ)
print("f(x, y) = %g" % f(x, y))