function _matrixNormInfinity (x) {
      // norm(x) = the largest row sum
      const r = []
      // result
      let maxr = 0
      // skip zeros since abs(0) == 0
      x.forEach(function (value, index) {
        const i = index[0]
        const ri = add(r[i] || 0, abs(value))
        if (larger(ri, maxr)) {
          maxr = ri
        }
        r[i] = ri
      }, true)
      return maxr
    }
Calculate the infinity norm for a matrix
@param {Matrix} x
@returns {number} Returns the norm
@private