CODEWITHSUNDEEP
pythonlistfunctionmatrixmatrix-multiplication
Kaushani Roy Chowdhury
Kaushani Roy Chowdhury

Reputation: 109

python: list index out of range in matrix multiplication

i'm new to python,so i'm sorry if this is a silly question. This is a legit program for matrix multiplication but i don't understand why it's throwing the error list index out of range for my input? 

def matmult(a,b):
 product=[[0 for i in range(len(a))] for j in range(len(b[0]))]
 for i in range(len(a)):
    for j in range(len(b[0])):
      for k in range(len(b)):
        product[i][j]+=a[i][k]*b[k][j]
 return product
matmult([[1,1]],[[3,4],[5,6]])

Upvotes: 1

Views: 1027

Answers (1)

Sagar B Hathwar
Sagar B Hathwar

Reputation: 536

It's because of product=[]. The product list is empty but you are indexing it. That is throwing the IndexError: list index out of range error

Do this instead

product = [[0 for i in range(len(b[0]))] for j in range(len(a))]

This will pre-allocate space for the product so that you can index it

Upvotes: 1

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