# function changing input value

The following code is supposed to implement a basic percolation process on a matrix of 0's and 1's. For some reason, it's changing the value of the matrix I input, and I can't figure out why. I'm sure it's a basic error on my part, but if someone can set me straight, I'd appreciate it!

Here's the function I defined:


n = 4;
def percolate(B):
update = B;
for i in [0..n-1]:
for j in [0..n-1]:
nbr_sum = 0;
if (i==0):
nbr_sum += B[i+1,j];
elif (i==n-1):
nbr_sum += B[i-1,j];
else:
nbr_sum += B[i-1,j]+B[i+1,j];
if (j==0):
nbr_sum += B[i,j+1];
elif (j==n-1):
nbr_sum += B[i,j-1];
else:
nbr_sum += B[i,j-1]+B[i,j+1];
if (nbr_sum > 1):
update[i,j] = 1;
return update;


When I execute


Bid = matrix.identity(n);
percolate(Bid)


I get the expected output


[1 1 0 0]
[1 1 1 0]
[0 1 1 1]
[0 0 1 1]


but the value of Bid also changes to the same value (as opposed to continuing to be the n x n identity matrix, as desired).

edit retag close merge delete

Use update = B.copy(), otherwise update is the same as B. By the way, no need for all these ;