RuntimeWarning: invalid value encountered in divide

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I have to make a program using Euler"s method for the "ball in a spring" model

from pylab import*
from math import*
m=0.1
Lo=1
tt=30
k=200
t=20
g=9.81
dt=0.01
n=int((ceil(t/dt)))
km=k/m
r0=[-5,5*sqrt(3)]
v0=[-5,5*sqrt(3)]
a=zeros((n,2))
r=zeros((n,2))
v=zeros((n,2))
t=zeros((n,2))
r[1,:]=r0
v[1,:]=v0
for i in range(n-1):
    rr=dot(r[i,:],r[i,:])**0.5
    a=-g+km*cos(tt)*(rr-L0)*r[i,:]/rr
    v[i+1,:]=v[i,:]+a*dt
    r[i+1,:]=r[i,:]+v[i+1,:]*dt
    t[i+1]=t[i]+dt

    #print norm(r[i,:])

plot(r[:,0],r[:,1])
xlim(-100,100)
ylim(-100,100)
xlabel("x [m]")
ylabel("y [m]")

show()

I keep getting this error:

a=-g+km*cos(tt)*(rr-L0)*r[i,:]/rr
RuntimeWarning: invalid value encountered in divide

I can"t figure it out, what is wrong with the code?

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Answer #1

import time
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Here is another example where something is run approximately once a minute:

import time
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Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

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Path objects from the Python 3.4+ pathlib module also expose these instance methods:

Is there a ceiling equivalent of // operator in Python?

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I found out about the // operator in Python which in Python 3 does division with floor.

Is there an operator which divides with ceil instead? (I know about the / operator which in Python 3 does floating point division.)

165

Answer #1

You can just do upside-down floor division:

def ceildiv(a, b):
    return -(-a // b)

This works because Python"s division operator does floor division (unlike in C, where integer division truncates the fractional part).

This also works with Python"s big integers, because there"s no (lossy) floating-point conversion.

Here"s a demonstration:

>>> from __future__ import division   # a/b is float division
>>> from math import ceil
>>> b = 3
>>> for a in range(-7, 8):
...     print(["%d/%d" % (a, b), int(ceil(a / b)), -(-a // b)])
... 
["-7/3", -2, -2]
["-6/3", -2, -2]
["-5/3", -1, -1]
["-4/3", -1, -1]
["-3/3", -1, -1]
["-2/3", 0, 0]
["-1/3", 0, 0]
["0/3", 0, 0]
["1/3", 1, 1]
["2/3", 1, 1]
["3/3", 1, 1]
["4/3", 2, 2]
["5/3", 2, 2]
["6/3", 2, 2]
["7/3", 3, 3]

We hope this article has helped you to resolve the problem. Apart from RuntimeWarning: invalid value encountered in divide, check other __del__-related topics.

Want to excel in Python? See our review of the best Python online courses 2023. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:



Javier Innsbruck

London | 2023-03-24

Maybe there are another answers? What RuntimeWarning: invalid value encountered in divide exactly means?. I just hope that will not emerge anymore

Boris Galleotti

Rome | 2023-03-24

I was preparing for my coding interview, thanks for clarifying this - RuntimeWarning: invalid value encountered in divide in Python is not the simplest one. I am just not quite sure it is the best method

Carlo OConnell

Tallinn | 2023-03-24

I was preparing for my coding interview, thanks for clarifying this - RuntimeWarning: invalid value encountered in divide in Python is not the simplest one. Checked yesterday, it works!

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