do not differentiate material by default
do not differentiate material by default

walshjon/openmc,liangjg/openmc,mit-crpg/openmc,liangjg/openmc,amandalund/openmc,wbinventor/openmc,walshjon/openmc,shikhar413/openmc,paulromano/openmc,shikhar413/openmc,amandalund/openmc,smharper/openmc,liangjg/openmc,paulromano/openmc,amandalund/openmc,liangjg/openmc,wbinventor/openmc,paulromano/openmc,wbinventor/openmc,walshjon/openmc,smharper/openmc,mit-crpg/openmc,mit-crpg/openmc,mit-crpg/openmc,smharper/openmc,shikhar413/openmc,paulromano/openmc,smharper/openmc,amandalund/openmc,walshjon/openmc,wbinventor/openmc,shikhar413/openmc