How to evaluate a function in Python using numpy arrays?

Question

I have two arrays of randomly generated x's and y's and I want to evaluate each pair at some function. How do I do that using numpy? I tried the code below, but it does not work.

What I want is an array of func(x_i,y_i).

x = np.random.uniform(0, 1, 100)
y = np.random.uniform(0, 1, 100)

func = np.array((math.exp(-2 * x) * math.cos(2 * y)))

Any ideas?

We like to see more than 'doesnt work'. We want to see the error, and if possible, to see you trying to understand the error. If the error occurs in long expression, try evaluating pieces to see exactly which is giving problems. Is it the np.array? or the math.cos(...)? — hpaulj
– hpaulj, Commented May 12, 2021 at 16:17
Spend more time reading numpy basics. Thinking in terms of evaluating single values or pairs as your math function requires, results in slow code. You want to become familiar with the operators and methods that work with whole arrays. The switch from math.cos to np.cos is just one example. — hpaulj
– hpaulj, Commented May 12, 2021 at 17:39

Camilo Martínez M. · Accepted Answer · 2021-05-12 16:17:42Z

1

Don't use math, use numpy.

import numpy as np

x = np.random.uniform(0, 1, 100)
y = np.random.uniform(0, 1, 100)

func = np.exp(-2 * x) * np.cos(2 * y)

>>> func.shape
    (100,)

That is, func[i] contains the result of your function using x[i] and y[i] as input.

edited May 12, 2021 at 16:17

answered May 12, 2021 at 16:15

Camilo Martínez M.

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4 Comments

hpaulj Over a year ago

What's the purpose of the np.array() wrapper?

Camilo Martínez M. Over a year ago

Oopss, one mistake due to copy/paste it.

Brasilian_student Over a year ago

How do I compare the values I have in the func variable with the values in the y variable? I tried indicator = (y <= func), but it does return anything

Camilo Martínez M. Over a year ago

Given the fact that y and func should now be numpy arrays, you can use any operation on them that numpy offers. For instance, comparison = y <= func makes comparison a boolean array of the same shape as y. What do you mean that it doesn't return anything?

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