![]() ![]() Knowing that Matlab will set every other entry as 0, you can do something like Adiag ( 7 3 1,2)+diag (2,4) in order to get 0 0 7 0 2 0 0 0 3 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 In other words youre creating two separate matrices with two diag () commands. This example shows how spdiags creates the diagonals when the columns of B are longer than the diagonals they are replacing. 1 Answer Sorted by: 2 You cannot set multiple diagonals using a unique diag () call. The statement = spdiags(A) produces d = ' andĬonversely, with the above B and d, the expression spdiags(B,d,7,4) reproduces the original A.Įxample 3. Turn it into Wilkinson's test matrix (see gallery): This example generates a sparse tridiagonal representation of the classic second difference operator on n points. They are not referenced when B is input and are set to zero when B is output.Įxample 1. Perhaps better in some applications is to create a sparse matrix, since a diagonal matrix is quite sparse. Some elements of B, corresponding to positions outside of A, are not defined by these loops. diag is the normal MATLAB solution (as pointed out by posdef.) Thus D diag (vec) gives you a matrix with diagonal elements as needed. The spdiags function deals with three matrices, in various combinations, as both input and output.Īn m-by- n matrix, usually (but not necessarily) sparse, with its nonzero or specified elements located on p diagonals.Ī min(m,n)-by- p matrix, usually (but not necessarily) full, whose columns are the diagonals of A.Ī vector of length p whose integer components specify the diagonals in A. If a column of B is longer than the diagonal it's replacing, spdiags takes elements of super-diagonals from the lower part of the column of B, and elements of sub-diagonals from the upper part of the column of B. The output is sparse.Ĭreates an m-by- n sparse matrix by taking the columns of B and placing them along the diagonals specified by d. Replaces the diagonals specified by d with the columns of B. ![]() d is a vector of length p whose integer components specify the diagonals in A. B is a min(m,n)-by- p matrix whose columns are the p nonzero diagonals of A. Four different operations, distinguished by the number of input arguments, are possible:Įxtracts all nonzero diagonals from the m-by- n matrix A. The spdiags function generalizes the function diag. Spdiags (MATLAB Functions) MATLAB Function ReferenceĮxtract and create sparse band and diagonal matrices ![]()
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