Duplication Issue with for Loop in Python

Question

How do I fix the issue of duplication in the following code? The first entry is the same as the second for example.

Input:
import numpy as np
t_max=np.arange(0,2.1,0.1)
for j in range (2,len(t_max)):
 time=np.arange(t_max[2],t_max[j]+0.1,0.1)
 print(time)
Output:
[0.2 0.3]
[0.2 0.3]
[0.2 0.3 0.4]
[0.2 0.3 0.4 0.5]
[0.2 0.3 0.4 0.5 0.6]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. ]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
 2. ]

• Kyle Parsons: Probably floating point errors in trying to hit the max of the arrange exactly. Try t_max[j] + 0.11 as the second parameter of the arange.

Answer 1

Just try using slicing:

import numpy as np
t_max=np.arange(0,2.1,0.1)
for j in range(4, len(t_max) + 1):
 time=t_max[2:j]
 print(time)

Output:

[0.2 0.3]
[0.2 0.3 0.4]
[0.2 0.3 0.4 0.5]
[0.2 0.3 0.4 0.5 0.6]
[0.2 0.3 0.4 0.5 0.6 0.7]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. ]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
 2. ]

Answer 2

This question is about why 0.1+0.2>0.3 in computer programming language.

In your case, when j=2 the code is turn to np.arrange(0.2, 0.2+0.1, 0.1).

There's code output below:

Input:
 a = np.arange(0.2,0.3,0.1)
 print(a)
Output:
 [0.2]
Input:
 a = np.arange(0.2,0.2+0.1,0.1)
 print(a)
 [0.2 0.3]

You can just simply use round to fix it in your case. Like this:

time=np.arange(t_max[2],round(t_max[j]+0.1,1),0.1)

Output:

[0.2]
[0.2 0.3]
[0.2 0.3 0.4]
[0.2 0.3 0.4 0.5]
[0.2 0.3 0.4 0.5 0.6]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. ]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9]
[0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.]