Numerical and symbolic calculations to solve linear algebraic equations

Implement the following functions in C/C++ language:

1. bool lu(double* a, int* pivot, int n); LU decomposition of matrix

2. bool guass(double const* lu, int const* p, double* b, int n); find the solution of linear algebraic equations

3. void qr(double* a, double* d, int n); QR decomposition of matrix

4. bool hshld(double const*qr, double const*d, double*b, int n); Seek the solution of linear algebraic equations