Some of the mex files use parallel programming using [http://openmp.org/wp/ OpenMp]:

Under linux some environment variables have to be defined to get the thing working because there is an incompatibility issue between the multithread library distributed with matlab (libguide.so) and the open source multithread library used by the gnu compiler (libgomp.so). The simplest workaround is to add the folowwing lines in your .bashrc file: 

export LD_PRELOAD=$LD_PRELOAD:/lib/libgcc_s.so.1
export LD_PRELOAD=$LD_PRELOAD:/usr/lib/libstdc++.so.6
export LD_PRELOAD=$LD_PRELOAD:/usr/lib/libgomp.so.1

The first two lines are necessary even without parallel programming.