re-activate parallelization for gram_matrix
re-activate parallelization for gram_matrix

nckz/bart,sdimoudi/bart,Takishima/bart,nckz/bart,sidward/bart,nckz/bart,mjacob75/bart,mrirecon/bart,grlee77/bart,sdimoudi/bart,Takishima/bart,Takishima/bart,frankong/bart,sidward/bart,nckz/bart,mrirecon/bart,mjacob75/bart,sidward/bart,Takishima/bart,sidward/bart,mjacob75/bart,mrirecon/bart,sidward/bart,sdimoudi/bart,grlee77/bart,frankong/bart,sdimoudi/bart,mjacob75/bart,Takishima/bart,frankong/bart,grlee77/bart,grlee77/bart,sdimoudi/bart,mrirecon/bart,grlee77/bart,mjacob75/bart,nckz/bart,mrirecon/bart,frankong/bart,frankong/bart