Segmentation fault in Cython - cython

Question

I am new to Cython. I have written a pyx file that returns a 2D Numpy or a memoryview array.
Here is the pyx code:
import numpy as np
import cython
cimport numpy as np
from libc.math cimport int
#cython.wraparound(False)
#cython.boundscheck(False)
#cython.cdivision(True)
#cython.nonecheck(False)
cdef class TwoDMatrix():
''' make a two dimensional matrix '''
cdef int N
def __init__(self,N):
self.N = N
cpdef twoD(self, int [:,:] vector,str array):
if array == 'numpy':
state = 2*np.random.randint(2,size=(self.N,self.N))-1
return state
else:
vec=self.initialise(vector,self.N)
return vec
cdef int [:,:] initialise(self, int [:,:] s,k) :
cdef int i,j
for i in range(k+1):
for j in range(k+1):
if np.random.rand() <0.5:
s[i,j] = -1
else:
s[i,j] = 1
return s
And here is the main py file where I give input:
import numpy as np
import main
def matrix():
N = 10
vector = main.TwoDMatrix(N)
spin = np.zeros((N,N),dtype=np.int32)
print(f"from numpy: {vector.twoD(spin,'numpy')}")
print(f"from memoryview: {vector.twoD(spin,'memoryview')}")
print("program successfully exited")
if __name__ == "__main__":
matrix()
The problem is for N >5 , when I run in terminal it always shows a segmentation fault(core dumped) message at the bottom. And for N>1, a similar following message is shown:
"corrupted size vs. prev_size while consolidating
Aborted (core dumped)"
Why is this message popping up? Is there anything that I should consider about memory allocation?

Answer 1

The segmentation fault is due to out-of-bounds accesses. Indeed, you create matrices of size (N,N) while initialise iterate over range range(0, k+1) where k=N. Thus you need to either use bigger matrices or to fix the two nested loops so to iterate over range(0, k) / range(0, N).