CODEWITHSUNDEEP
matlabmatrix
bdhvevhvonof
bdhvevhvonof

Reputation: 467

matlab: how to create matrix by shift vector

I have row and column in matlab:

a = [1 0 3 ... a_k]; - row 1xk

b = [1;0;3; ... b_k]; - column kx1

I want to create new matrix's (A and B) mxn, that can be populate by shift row and column:

A = [1 0 3 0 0 0 0 ... 0;
     0 1 0 3 0 0 0 ... 0;
     0 0 1 0 3 0 0 ... 0;
     ...
     0 0 0 0 0 0 ... 1 0 3 ]

B=  [1 0 0 0 0 0 0 ... 0;
     0 1 0 0 0 0 0 ... 0;
     3 0 1 0 0 0 0 ... 0;
     0 3 0 1 0 0 0 ... 0;
     0 0 3 0 1 0 0 ... 0;
     ... 
     0 0 0 0 0 0 0 ... 3]

How can I do it?

Upvotes: 0

Views: 889

Answers (2)

Luis Mendo
Luis Mendo

Reputation: 112659

Is this what you want?

>> a = [1 0 3];
>> m = 5; %// number of rows
>> A = convmtx(a,m)
A =
     1     0     3     0     0     0     0
     0     1     0     3     0     0     0
     0     0     1     0     3     0     0
     0     0     0     1     0     3     0
     0     0     0     0     1     0     3

>> b = [1;0;3];
>> m = 4; %// number of columns
>> B = convmtx(b,m)
B =
     1     0     0     0
     0     1     0     0
     3     0     1     0
     0     3     0     1
     0     0     3     0
     0     0     0     3

Upvotes: 1

MrAzzaman
MrAzzaman

Reputation: 4768

You can do this in a slightly tricky way by using a combination of indexing and bsxfun. First we want to create an index matrix that represents the shift that we're trying to. It should look like this (at least for A):

1  2  3  4 ...  k
k  1  2  3 ...  k-1
etc

To create this, we can use bsxfun as follows:

index = mod(bsxfun(@plus,1:k,-(1:(k-2))'),k)+1;

We can then create the matrix A by using this as an index matrix for a:

A = a(index);

The matrix B is the same, just transposed:

B = b(index)';

Upvotes: 1

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