CODEWITHSUNDEEP
pythongauss
James
James

Reputation: 21

Python Gauss Elimination

Super New to programming and still learning how to debug. Every time I run this program for Gauss elimination I get

"line 16, in GaussElim tmp=A[maxRow][k] IndexError: list index out of range"

I think it mean the code is stepping over the limit of the index, but I am not sure on how to correct it. Any advice would be much appreciated thank you!

def GaussElim(A):
n=len(A)

for i in range(0,n):   #search for maximum in this column
    maxE1=abs(A[i][i])
    maxRow=i
    for k in range(i+1,n):
        if abs(A[k][i])>maxE1:
            maxE1=abs(A[k][i])
            maxRow=k
            # swap maximum row with current row (column by column)
    for k in range(i,n+1):
        tmp=A[maxRow][k]
        A[maxRow][k]=A[i][k]
        A[i][k]=tmp

    for k in range(i+1,n):
        c=-A[k][i]/A[i][i]
        for j in range(i,n+1):
            if i==j:
                A[k][j]=0
            else:
                A[k][j]+=c*A[i][j]
                #solve equation Ax+b for an upper triangular matrix A
x=[0 for i in range(n)]
for i in range(n-1,-1,-1):
    x[i]=A[i][n]/A[i][i]
    for k in range(i-1,-1,-1):
        A[k][n]-=A[k][i]*x[i]
return x

def main():
A=[[2,7,3,6,2],
        [3,3,4,4,6],
        [6,9,5,3,3],
        [6,9,5,3,3],
        [4,2,1,7,5]]

mysum1 = GaussElim(A)
print('a) GaussElimination Solution = {:.1f}'.format(mysum1))

Upvotes: 2

Views: 3917

Answers (1)

philngo
philngo

Reputation: 931

In python, lists are zero indexed. If you print the value of k, you'll see you're getting a value k=5, which is presumably coming from your range(i, n+1) (where n=5). Your 5x5 array will only support indexing from 0 to 4.

Upvotes: 0

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