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Section: Sparse Matrix Support
Plots the sparsity pattern of a sparse matrix. The syntax for its use is
spy(x)
which uses a default color and symbol. Alternately, you can use
spy(x,colspec)
 where colspec is any valid color and symbol spec accepted by plot. 
First, an example of a random sparse matrix.
--> y = sprand(1000,1000,.001); --> spy(y,'ro')
which is shown here
 
spy to visualize the structure.
--> A = sparse(1000,1000); --> for i=1:25; A((1:40) + 40*(i-1),(1:40) + 40*(i-1)) = 1; end; --> spy(A,'gx')
with the result shown here
