how to put an array into a matrix

Hi there!

the function "triu(X,1)" returns the upper trangular part of the matrix X. I now have an array of size 1-by-(0.5*n*(n-1)), exactly the number of elements in the upper triangular. How can I, without using any loop, put this array into a n-by-n matrix so that this matrix is what triu(X,1) returns?

Thanks. Lianovich

Answer 1

[Walter Roberson]

n = floor(sqrt(2*length(V)));
M = zeros(n);
M(logical(triu(ones(n),1))) = V;

[Matt Fig]

I believe Walter meant:

n = floor(sqrt(2*length(V))) + 1

[Chien-Chia Huang]

Thanks Walter.

But when I tried to put [1 2 3] into a 3-by-3 square matrix, the error message occured:

??? In an assignment A(I) = B, the number of elements in B and

I must be the same.

Error in ==> arraytomatrix at 9

M(logical(triu(ones(n),1))) = V;

Guess I must have mistaken what you meant.

What should the V be?

[Chien-Chia Huang]

Yup, Matt is right.

Thanks, Matt.