I need to solve to solve a "large" symmetric sparse linear systems, with matrix size 8000?
I heard about HSL, ITPACK, but I don't know how to use them, and I am working in C language.
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You haven't told us whether your matrix is positive definite or not- this is a very important factor in selecting a solver. You also haven't told us whether the matrix is well conditioned or poorly conditioned. A third important question is whether you need a fairly accurate solution (e.g. accurate to 10 digits) or whether a less accurate solution (e.g. accurate to 4 or 5 digits) would be acceptable.
However, for matrices of this small size (8,000 by 8,000 is quite small by contemporary standards) you should probably be using a direct factorization method rather than an iterative method. Furthermore, unless you have a lot of these systems to solve it probably isn't worth the added programming effort to use a sparse direct factorization method. Thus I'd suggest storing the matrix in dense form and using LAPACK (and in particular because of its C language bindings the CLAPACK package) to solve your system of equations.
If you're willing to invest somewhat more time and effort in coding this, and if you're concerned about the performance of the dense matrix implementation then you might consider using the sparse direct factorization approach as implemented (for example) in the SuiteSparse package written by Timothy Davis.