Putting together a larger matrix from smaller matrices

Scott David Daniels Scott.Daniels at Acm.Org
Tue Aug 25 17:26:44 CEST 2009


Matjaz Bezovnik wrote:

If you are using numpy (which it sounds like you are):

IDLE 2.6.2
 >>> import numpy as np
 >>> v = np.array([[0,1,2],[3,4,5],[6,7,8]], dtype=float)
 >>> v
array([[ 0.,  1.,  2.],
        [ 3.,  4.,  5.],
        [ 6.,  7.,  8.]])
 >>> w = np.array([[10,11,12],[13,14,15],[16,17,18]], dtype=float)
 >>> w
array([[ 10.,  11.,  12.],
        [ 13.,  14.,  15.],
        [ 16.,  17.,  18.]])
 >>> r = np.zeros((6,6))
 >>> r
array([[ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.]])
 >>> r[:3,:3] = v
 >>> r
array([[ 0.,  1.,  2.,  0.,  0.,  0.],
        [ 3.,  4.,  5.,  0.,  0.,  0.],
        [ 6.,  7.,  8.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.],
        [ 0.,  0.,  0.,  0.,  0.,  0.]])
 >>> r[3:,3:] = w
 >>> r
array([[  0.,   1.,   2.,   0.,   0.,   0.],
        [  3.,   4.,   5.,   0.,   0.,   0.],
        [  6.,   7.,   8.,   0.,   0.,   0.],
        [  0.,   0.,   0.,  10.,  11.,  12.],
        [  0.,   0.,   0.,  13.,  14.,  15.],
        [  0.,   0.,   0.,  16.,  17.,  18.]])
 >>>

In general, make the right-sized array of zeros, and at various points:
and you can ssign to subranges of the result array:

     N = 3
     result = np.zeros((len(parts) * N, len(parts) * N), dtype=float)
     for n, chunk in enumerate(parts):
         base = n * 3
         result[base : base + 3, base : base + 3] = chunk

--Scott David Daniels
Scott.Daniels at Acm.Org



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