===== GNU Scientific Library (GSL/FGSL) =====

==== Documentation and Examples of the GSL ====
https://en.wikipedia.org/wiki/GNU_Scientific_Library


==== Documentation of the FGSL ====

Not realy something anywhere.

http://www.lrz.de/services/software/mathematik/gsl/fortran/

===Sorting===
<code fortran>
program mysort
  use fgsl
  use iso_c_binding
  implicit none
  integer(c_size_t) :: i, n idx(20)
  double precision :: arr(20)

  ...

  ! index sort. Original contents undisturbed
  call fgsl_sort_index(idx, arr, 1_fgsl_size_t, n)
  idx = idx +1 
  do i = 1, n ! array will be shown numerical order
     write (*, fmt = ifmt) sects(idx(i))
  enddo
</code>

For sorting in place, see links.

==Stats==
<code fortran>
program stats
  use fgsl 
  implicit none
  real(fgsl_double) :: data(5) = (/17.2D0, 18.1D0, 16.5D0, 18.3D0, 12.6D0 /)
  real(fgsl_double) :: mean, variance, largest, smallest

  mean     = fgsl_stats_mean(data, 1_fgsl_size_t, 5_fgsl_size_t)
  variance = fgsl_stats_variance(data, 1_fgsl_size_t, 5_fgsl_size_t)
  largest  = fgsl_stats_max(data, 1_fgsl_size_t, 5_fgsl_size_t)
  smallest = fgsl_stats_min(data, 1_fgsl_size_t, 5_fgsl_size_t)  
end program stats
</code>