RuntimeWarning invalid value encountered in divide

Question

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

User · Answer

Python indexing starts at 0  rather than 1   so your assignment  r 1      r0  defines the second  i e  index 1  element of r and leaves the first  index 0  element as a pair of zeros  The first value of i in your for loop is 0  so rr gets the square root of the dot product of the first entry in r with itself  which is 0   and the division by rr in the subsequent line throws the error

User · Answer

I think your code is trying to  divide by zero  or  divide by NaN   If you are aware of that and don t want it to bother you  then you can try   import numpy as np np seterr divide  ignore   invalid  ignore     For more details see    http   docs scipy org doc numpy reference generated numpy seterr html

User · Answer

You are dividing by rr which may be 0 0  Check if rr is zero and do something reasonable other than using it in the denominator

User · Answer

To prevent division by zero you could pre-initialize the output  out  where the div0 error happens  eg np where does not cut it since the complete line is evaluated regardless of condition   example with pre-initialization   a   np arange 10  reshape 2 5  a 1 3    0 print a        0 1 2 3 4    5 6 7 0 9   a 0  a 1      errors at 3 0 out   np ones   5      preinit np divide a 0  a 1   out out  where a 1   0   only divide nonzeros else 1

[python] RuntimeWarning: invalid value encountered in divide

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