On Sun, 5 Sep 2004, Stephen Walton wrote:
On Sun, 2004-09-05 at 02:44, Karthikesh Raju wrote:
example a = reshape(arange(0,18),(2,3,3))
a[0,:,:], a[1,:,:] should be rows wise extracts like
a[0,:,:] = 0 3 6 1 4 7 2 5 8
I'm not certain why you expect the transpose of the actual result here. There are two possibilities. MATLAB arrays are column major (first index varies most rapidly), so in MATLAB (one-based indexing):
The transpose was another person's reply to the above question. Actually, the reason i was doing all this was because i was working on "a dataloader" that allowed me to dump and load variables in a ascii text file, similar to what Matlab's mat format does. This worked fine as long as the array dimension was 2. Now i need 3D array support, and one idea was to convert all the dimensions into a tuple, load the data and reshape as per my the array dimension requirement. Obviously, both being different (column major vs row major), i elements would be wrong. Hence i wanted to see if reshape could have a flag, that told it to do either row wise or column wise reshaping. A partial support for 3D has been by extending the number of columns in a 2D matrix, so each new dimension is a block matrix in the columns. This works fine, but again another day when i need 4D it would break. This is why i thought i could play with reshape to get things correct once and for all. Warm regards karthik
A=reshape([0:17],[2,3,3]); M=reshape(A(1,:,:),[3,3]) M =
0 6 12 2 8 14 4 10 16
This is the same thing you would get in MATLAB from M=reshape([0,2,4,6,8,10,12,14,16],[3,3])
numarray arrays are row major (last index varies most rapidly), so in numarray:
A=reshape(arange(0,18), (2,3,3)) M=A[0,:,:] M array([[0, 1, 2], [3, 4, 5], [6, 7, 8]])
This is the same thing you get for M=reshape(arange(0,9),(3,3)).
-- Stephen Walton <stephen.walton@csun.edu> Dept. of Physics & Astronomy, Cal State Northridge