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Sparse symmetric random matrix

`R = sprandsym(S)R = sprandsym(n,density)R = sprandsym(n,density,rc)R = sprandsym(n,density,rc,kind)R = sprandsym(S,[],rc,3)`

`R = sprandsym(S)` returns
a symmetric random matrix whose lower triangle and diagonal have the
same structure as `S`. Its elements are normally
distributed, with mean `0` and variance `1`.

`R = sprandsym(n,density)` returns
a symmetric random, `n`-by-`n`,
sparse matrix with approximately `density*n*n` nonzeros;
each entry is the sum of one or more normally distributed random samples,
and (`0 <= density <= 1`).

`R = sprandsym(n,density,rc)` returns
a matrix with a reciprocal condition number equal to `rc`.
The distribution of entries is nonuniform; it is roughly symmetric
about 0; all are in [−1,1].

If `rc` is a vector of length `n`,
then `R` has eigenvalues `rc`. Thus,
if `rc` is a positive (nonnegative) vector then `R` is
a positive (nonnegative) definite matrix. In either case, `R` is
generated by random Jacobi rotations applied to a diagonal matrix
with the given eigenvalues or condition number. It has a great deal
of topological and algebraic structure.

`R = sprandsym(n,density,rc,kind)`
is positive definite.

If kind = 1,

`R`is generated by random Jacobi rotation of a positive definite diagonal matrix.`R`has the desired condition number exactly.If kind = 2,

`R`is a shifted sum of outer products.`R`has the desired condition number only approximately, but has less structure.

`R = sprandsym(S,[],rc,3)` has the same structure
as the matrix `S` and approximate condition number `1/rc`.

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