Python: TypeError: only length-1 arrays can be converted to Python scalars

Question

I have a func

f(x) = sin(x/5.0)*exp(x/10.0) + 5*exp(-x/2.0)

I need to solve system of linear equations

w0 + w1x1 + w2(x1)**2 + ... + wn(x1)**n = f(x1)

I solve that but I have a problem with plot it

from math import sin, exp
from scipy import linalg
import numpy as np

b = []
def f(x):
    return sin(x/5.0)*exp(x/10.0) + 5*exp(-x/2.0)

for i in [1, 15]:
    b.append(f(i))

A = []

for i in [1, 15]:
    ij = []
    x0 = i ** 0
    x1 = i ** 1
    ij.append(x0)
    ij.append(x1)
    A.append(ij)

matrix = np.array(A)
b = np.array(b).T

x = linalg.solve(matrix, b)
from matplotlib import pyplot as plt
plt.plot(x, f(x))

But it returns

TypeError: only length-1 arrays can be converted to Python scalars

How can I solve this problem?

unutbu · Accepted Answer · 2017-08-20 19:36:46Z

3

math.sin and math.exp expect scalar inputs. If you pass an array, you get a TypeError

In [34]: x
Out[34]: array([ 3.43914511, -0.18692825])

In [35]: math.sin(x)
TypeError: only length-1 arrays can be converted to Python scalars

from math import sin, exp loads sin and exp from the math module and defines them as functions in the global namespace. So f(x) is calling math's version of the sin function on x which is a NumPy array:

def f(x):
    return sin(x/5.0)*exp(x/10.0) + 5*exp(-x/2.0)

To fix the error, use NumPy's sin and exp functions instead.

import numpy as np
def f(x):
    return np.sin(x/5.0)*np.exp(x/10.0) + 5*np.exp(-x/2.0)

edited Aug 20, 2017 at 19:36

answered Aug 20, 2017 at 19:23

unutbu

886k197 gold badges1.9k silver badges1.7k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Petr Petrov Over a year ago

Why does it happen?

unutbu Over a year ago

The functions in the math module from the standard library expects scalars as inputs. The equivalent NumPy functions are designed to work with NumPy arrays. x is a NumPy array, so you need to use np.sin(x), not math.sin(x).

Collectives™ on Stack Overflow

Python: TypeError: only length-1 arrays can be converted to Python scalars

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related