CODEWITHSUNDEEP
pythonmath
mamidon
mamidon

Reputation: 895

How to avoid a seemingly unavoidable divide by zero

Ok, so I'm doing the power method in python.

Basically, the equation revolves around multiplying a matrix A by a vector (y) like this:

for i in range(0, 100):

    y = mult(matrix,y)

    y = scalarMult(y, 1.0/y[0][0])

Then you multiply the vector y by 1/(the first element in y). Now, if the matrix is sparse or has a zero in just the right spot, you will get a zero for the first element in a. None of my googling skills have yielded a modification to the power method to avoid this.

For those interested, I'm trying to solve for the eigenvalues of a matrix; and my code works as long as there aren't too many zeros.

Upvotes: 2

Views: 873

Answers (1)

Rok
Rok

Reputation: 494

Instead of dividing by first element of the vector you can divide by one of its norms. For example if you use second norm, the length of the vector will always be 1. 

norm = sum(e**2 for e in y)**0.5

Norm of the vector is only zero when vector is 0 (has all elements 0), so division by 0 should not happen.

Upvotes: 3

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