Home  |  About Us  |  Link To Us  |  FAQ  |  Contact

# SUB2IND4UP Linear index from subscripts of upper triangular matrix (only elements above diagonal) 1.0

Date Added: July 06, 2013  |  Visits: 192

IND = SUB2IND4UP(I, J) returns the linear index equivalent to the row and column subscripts I and JLet ind be a vector of indexes for entries of some upper triangular matrix. The entries are selected vertically so that: ind = 1 is associated to entry (1, 2) ind = 2 is associated to entry (1, 3) ind = 3 is associated to entry (2, 3) ind = 4 is associated to entry (1, 4) ... ind = N * (N - 1) / 2 is associated to entry (N - 1, N)***********************************************************************EXAMPLEIf A = rand(10);and b = A(find(triu(A, 1)));then, given subscripts I = [1:9];and J = [2:10];for matrix A, these are equivalent to indices IND = sub2ind4up(I, J);for vector b. In fact: all(A(sub2ind(size(A), I, J)) == b(IND)')ans = 1This is obtained without even knowing about size(A)***********************************************************************See also SUB2IND, IND2SUB, FIND.

 Requirements: No special requirements Platforms: Matlab Keyword: Afindtriua,  Allasub Indsizea,  Ind,  Ind Upi,  Indices,  Obtained,  Rand Users rating: 0/10