To make SHTns known by your C program, add

#include <fftw3.h>

#include <shtns.h>

in the preamble of your source file.

First of all you need to initialize SHTns. There are two ways to do this :

calling shtns_init function,
or calling shtns_create followed by shtns_set_grid or shtns_set_grid_auto. This way lets you choose normalization and optimization.

Multi-threaded transforms can be enabled (if available, see Compiling and installing SHTns) by a call to shtns_use_threads before shtns_init or shtns_create.

Then you must allocate some memory (with fftw_malloc so that the memory is properly aligned for vectorized code), and finally you can perform some spherical harmonic transforms.

See Also: Look at shtns.h for the function definitions and documentation.; See the C example for a simple usage of SHTns in a C program.

When your program is ready, compile it adding these options to the compiler (gcc) :

-L/path/to/lib/ -I/path/to/include/ -lshtns -lfftw3 -lm