CODEWITHSUNDEEP
pythonnumpy
Tianyi He
Tianyi He

Reputation: 1

I met an Error: line 21, in <module> ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

import numpy as np
Q = np.loadtxt(open("D:\data_homework_4\Q.csv","rb"), delimiter = ",", skiprows = 0)
b = np.loadtxt(open("D:\data_homework_4\B.csv","rb"), delimiter = ",", skiprows = 0)

def f(x):
    return 1/2 * x.T @ Q @ x + b.T @ x

def gradient(x):
    return Q @ x - b

n = 2000
x_t = np.zeros((100, 1))
alpha = 0.1
beta = 0.3
eta_t = 3.887e-6

for t in range(n + 2):
    g_t = gradient(x_t)
    k = 0
    while True:
        if f(x_t - beta**k * g_t) <= f(x_t) - alpha * beta**k * np.linalg.norm(g_t)**2:
            eta_t = beta**k
            break
        k += 1
    x_t -= eta_t * g_t
print(x_t)

line 21 is

if f(x_t - beta**k * g_t) <= f(x_t) - alpha * beta**k * np.linalg.norm(g_t)**2:

Q is 100x100, b is 100x1, x is 100x1. I looked up similiar errors, but none of them are like mine. Can somebody help me with this error. Thank you.

Upvotes: 0

Views: 159

Answers (1)

Partha Mandal
Partha Mandal

Reputation: 1441

As it says, in the if condition you are comparing between 2 arrays - both of which has multiple values and the if condition evaluates all of them but doesn't know how to collapse them into a single value of Truth - that's why it's asking you to use any or all:

Try this for example :

import numpy as np
arr = np.array([2,3])
arr1 = np.array([1,4])
arr, arr1

if (arr<arr1):
    pass

It would give you the same error that you have.

And to solve that I've added an all condition so that all the elements in those arrays have to satisfy the < condition

So:

import numpy as np
arr = np.array([2,3])
arr1 = np.array([1,4])
arr, arr1

if (arr<arr1).all():
    pass

Think about what makes sense in your case and use that (be it any or all)

Upvotes: 1

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