lib/sbm.js
function(sbm) {
    return _.sum(_.map(sbm.data, function (ar) { return ar.length }))
  }
function(sbm) {
    return _.sum(_.map(sbm.data, function (ar) { return ar.length }))
  }
function ( sbm ) { return _ . sum ( _ . map ( sbm . data , function ( ar ) { return ar . length } ) ) }
returns the number of 1 in the matrix
returns the number of 1 in the matrix