Updating a matrix in a time interval inside a for loop

[deanhystad]

Use python tags when posting code. I think I know what your program does, but without any indentation I cannot be sure.

If you want to keep P for each interval, why not do it this way:

L=3
N=30
Interval=10  # < Typo?  should be interval?
VB=[]
for nstep in np.arange(N):
    V=[]
    for i in range(0,L):
        U=[]
        for j in range(0,L):
            m=i+4*(i)*j*nstep-5*j*i
            U.append(m)
        V.append(U)
    VB.append(V)

at_intervals = []
K=np.array(VB)
P=np.zeros((1,L,L))
for i in range(0,N):
    for j in range(0,L):
        for k in range(0,L):
            if (K[i][j][k]>P[0][j][k]and(i%interval!=0)):
                P[0][j][k]=K[i][j][k]
                at_intervals.append(copy(P))