I followed the build instructions for S2Kit, using Macports's FFTW. S2Kit built and tested ok from command line. Testing the integration in Yawtb, I encountered a linker error:
>> yademo s2fst
% Sample(s) of code for S2FST
>> [phi,theta] = sphgrid(46,46); %%
>> mat = exp(-tan(theta/2).^2) .* ( phi == phi(1,10)); %%
>> fmat = s2fst(mat); %%
??? Invalid MEX-file '/IM2sandbox/yawtb/interfaces/s2kit/s2fst.mexmaci':
dlopen(/IM2sandbox/yawtb/interfaces/s2kit/s2fst.mexmaci, 1): Library not loaded: /opt/local/lib/libfftw3.3.dylib
Referenced from: /IM2sandbox/yawtb/interfaces/s2kit/s2fst.mexmaci
Reason: Incompatible library version: s2fst.mexmaci requires version 6.0.0 or later, but libfftw3.dylib provides version
Error in ==> yademo at 77
Some googling after (see comments here), I learned that this comes from a version mismatch between Matlab's FFTW and the newer Macports version.
Contrary to Geoffrey, I decided to update the lib in Matlab (quite similarly to the suggestion here). Note: a backup is recommended. In my case, the fix implied copying libfftw3.dylib and libfftw3.dylib from /opt/local/lib to /Applications/MATLAB_R2008b.app/bin/maci/ .
And now, the yademo s2fst example works great :-)
Note that I did not check whether this fix breaks other FFTW related code. YMMV.