1 dimensions: FFTW on vector of size 10 
  Error norm of |x - z1| 7.23451

 2 dimensions: FFTW on vector of size 100 
  Error norm of |x - z1| 74.7894

 3 dimensions: FFTW on vector of size 1000 
  Error norm of |x - z1| 739.169

 4 dimensions: FFTW on vector of size 10000 
  Error norm of |x - z1| 7661.66