1.This function is to solve Ax=b by conjugated gradient algorimth.
2.This program is written based on BLAS functions in gsl library.
3.This program reads a file containing MatrixFileName VectorFileName.Then it redirects to the file containing the elements of matrix and vectors. 
4.In the file containing the matrix or vector elements,the first row is the dimension of the matrix or vector.
5.The code should be able to be run as "MyProg < in > out";
6.If the matrix is a positive definite symmetric matrix, then the check part Ax should be equal or very close to b. But if A is singular, then there would be more than on answer to Ax=b, then the check part Ax would be quite different than b.