Python numpy loop index out of bounds error

Question

a1 = np.random.random_sample(10)

a2 = np.random.random_sample(5)

a3 = np.zeros([10])


for i in range(0,9):

    a3[i] = ((a2[i]+a2[i+1])/2.) * ((a1[i+1]-a1[i])/2.) * (a1[i]*a2[i])

    print(i, a3[i])

I tried to run this simple script and I get the error "IndexError: index out of bounds" ... Please any idea to avoid this error? I understand that the error caused by the number 5, but I can't change that as the a2 array is loaded from a txt (a2= np.loadtxt('data.txt',unpack=True, usecols=[1]) which its length is 5 Please any idea?

Grijesh Chauhan · Accepted Answer · 2013-03-20 15:24:43Z

1

There is only 5 elements in a2 because:

a2 = np.random.random_sample(5)

but in for loop runs for i > 5 upto 8

for i in range(0,9):

    a3[i] = ((a2[i]+a2[i+1])/2.) * ((a1[i+1]-a1[i])/2.) * (a1[i]*a2[i])
                       ^ index out                                ^ index out

because you access a2 as a2[i+1] also. So i can be at most 3 try with range(0,4)

EDIT:

To fill five extra 1s do like:

a2.extend(5*[1])
a2

edited Mar 20, 2013 at 15:24

answered Mar 20, 2013 at 4:54

Grijesh Chauhan

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5 Comments

user1640255 Over a year ago

yes I know the problem... any idea what to do for make this script running? (adding zeros to a2, and increasing its length? )

Grijesh Chauhan Over a year ago

@user1640255 Added an ides give it a try

user1640255 Over a year ago

I CANT change range(0,9)! ... and also in another part of my script the a2 has length 15, greater that others... whats then? Do I have add zeros to other arrays? Any other idea?

Grijesh Chauhan Over a year ago

@user1640255 Yes increase a2 size with 0 or 1 although I don't know what is your algo

user1640255 Over a year ago

any idea how to do that? is a secret?

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