this abstract does it
#calculate the sum of the reaction in a table
sum_reac=POST_RELEVE_T(ACTION=_F(INTITULE='somme_reactions',
GROUP_NO=('apppot','appmt',),RESULTAT=statnl,NOM_CHAM='REAC_NODA',
LIST_INST=listr,
RESULTANTE=('DX','DY','DZ',),OPERATION='EXTRACTION',),);
#print the table in the .resu file
IMPR_TABLE (TABLE=sum_reac,)
#print the table in the file declared (in ASTK) with LU=9 with the format of a tableau
IMPR_TABLE (TABLE=sum_reac, UNITE=9, FORMAT='TABLEAU',INFO=1,)