for multigroup fission matrix does not have same nonzero pattern as destruction matrix, fixed PETSC flag
for multigroup fission matrix does not have same nonzero pattern as destruction matrix, fixed PETSC flag

mit-crpg/openmc,lilulu/openmc,mit-crpg/openmc,smharper/openmc,smharper/openmc,kellyrowland/openmc,samuelshaner/openmc,nhorelik/openmc,samuelshaner/openmc,paulromano/openmc,paulromano/openmc,johnnyliu27/openmc,smharper/openmc,sxds/opemmc,shikhar413/openmc,walshjon/openmc,lilulu/openmc,wbinventor/openmc,shenqicang/openmc,mjlong/openmc,shenqicang/openmc,liangjg/openmc,sxds/opemmc,bhermanmit/cdash,johnnyliu27/openmc,keadyk/openmc_mg_prepush,walshjon/openmc,amandalund/openmc,kellyrowland/openmc,samuelshaner/openmc,amandalund/openmc,amandalund/openmc,johnnyliu27/openmc,wbinventor/openmc,smharper/openmc,bhermanmit/openmc,wbinventor/openmc,wbinventor/openmc,liangjg/openmc,bhermanmit/openmc,shikhar413/openmc,liangjg/openmc,mjlong/openmc,shikhar413/openmc,samuelshaner/openmc,amandalund/openmc,shikhar413/openmc,keadyk/openmc_mg_prepush,lilulu/openmc,walshjon/openmc,paulromano/openmc,keadyk/openmc_mg_prepush,walshjon/openmc,paulromano/openmc,johnnyliu27/openmc,mit-crpg/openmc,mit-crpg/openmc,liangjg/openmc,nhorelik/openmc