Here's an interesting question :)
I have two "vectors of matrices" which I want to tile like the hankel funct开发者_JAVA技巧ion does for regular vertices. For example: Column Vector:
10
00
20
00
30
00
Row vector:
30 40 50 60
00 00 00 00
The resulting matrix needs to be:
10 20 30 40
00 00 00 00
20 30 40 50
00 00 00 00
30 40 50 60
00 00 00 00
Note that the 0 values can be changed, the resulting structure is the important part.
A related question: I looked in the command "edit repmat" and saw some interesting syntax I couldn't find help for:
A=[1,3;2,4];
X=[1,1;2,2];
B=A(X,X);
and B ends up being
1 3 1 3
2 4 2 4
1 3 1 3
2 4 2 4
which is basically repmat(A,2,2);
So my question is, what is this syntax: A(X,X)?
Thanks a lot!
Ofer
If you want to tile a set of matrices the way HANKEL tiles values, here's one way you can do it. First, you can put all of your unique matrices in one cell array:
mat = [1 0; 0 0];
cArray = {mat 2.*mat 3.*mat 4.*mat 5.*mat 6.*mat}; %# Your 6 unique matrices
Now, if you want the first 3 matrices running down the first column and the last 4 matrices running across the last row, you can create an index matrix using HANKEL:
>> index = hankel(1:3,3:6);
index =
1 2 3 4
2 3 4 5
3 4 5 6
Then index your cell array with index
and use CELL2MAT to convert the resulting cell array to one matrix:
>> cell2mat(cArray(index))
ans =
1 0 2 0 3 0 4 0
0 0 0 0 0 0 0 0
2 0 3 0 4 0 5 0
0 0 0 0 0 0 0 0
3 0 4 0 5 0 6 0
0 0 0 0 0 0 0 0
For the second part of your question, when you perform an indexing operation like A(X,Y)
, you are using the elements of X
as row indices and the elements of Y
as column indices into A
. Every combination of values in X
and Y
is used. So, if X = [x1 x2 x3 x4]
and Y = [y1 y2 y3 y4]
, then the result of B = A(X,Y)
is equivalent to:
B = [A(x1,y1) A(x1,y2) A(x1,y3) A(x1,y4); ...
A(x2,y1) A(x2,y2) A(x2,y3) A(x2,y4); ...
A(x3,y1) A(x3,y2) A(x3,y3) A(x3,y4); ...
A(x4,y1) A(x4,y2) A(x4,y3) A(x4,y4)];
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