Initialize empty matrix in Python
What about initializing a list, populating it, then converting to an array.
demod4 = []
Or, you could just populate at initialization using a list comprehension
demod4 = [[func(i, j) for j in range(M)] for i in range(N)]
Or, you could initialize an array of all zeros if you know the size of the array ahead of time.
demod4 = [[0 for j in range(M)] for i in range(N)]
or
demod4 = [[0 for i in range(M)]*N]
Or try using numpy
.
import numpy as np
N, M = 100, 5000
np.zeros((N, M))
If you are using numpy
arrays, you initialize to 0, by specifying the expected matrix size:
import numpy as np
d = np.zeros((2,3))
>>> d
[[ 0. 0. 0.]
[ 0. 0. 0.]]
This would be the equivalent of MATLAB 's:
d = zeros(2,3);
You can also initialize an empty array, again using the expected dimensions/size
d = np.empty((2,3))
If you are not using numpy, the closest somewhat equivalent to MATLAB's d = []
(i.e., a zero-size matrix) would be using an empty list and then
append values (for filling a vector)
d = []
d.append(0)
d.append(1)
>>> d
[0, 1]
or append lists (for filling a matrix row or column):
d = []
d.append(range(0,2))
d.append(range(2,4))
>>> d
[[0, 1], [2, 3]]
See also:
initialize a numpy array (SO)
NumPy array initialization (fill with identical values) (SO)
How do I create an empty array/matrix in NumPy? (SO)
NumPy for MATLAB users
You could use a nested list comprehension:
# size of matrix n x m
matrix = [ [ 0 for i in range(n) ] for j in range(m) ]