MATLAB Mathematics - SERC - Index of

6 Sparse Matrices
Now F = full(S) displays the corresponding full matrix.
F = full(S)
F =
-2 1 0 0 0
1 -2 1 0 0
0 1 -2 1 0
0 0 1 -2 1
0 0 0 1 -2
Creating Sparse Matrices from Their Diagonal Elements
Creating sparse matrices based on their diagonal elements is a common
operation, so the function spdiags handles this task. Its syntax is
S = spdiags(B,d,m,n)
To create an output matrix S of size m-by-n with elements on p diagonals:
• B is a matrix of size min(m,n)-by-p. The columns of B are the values to
populate the diagonals of S.
• d is a vector of length p whose integer elements specify which diagonals of S
to populate.
That is, the elements in column j of B fill the diagonal specified by element j
of d.
Note If a column of B is longer than the diagonal it’s replacing,
super-diagonals are taken from the lower part of the column of B, and
sub-diagonals are taken from the upper part of the column of B.
As an example, consider the matrix B and the vector d.
B = [ 41 11 0
52 22 0
63 33 13
74 44 24 ];
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