code: function frob(a) {
    return Math.sqrt(
        a[0]*a[0]
      + a[1]*a[1]
      + a[2]*a[2]
      + a[3]*a[3]
      + a[4]*a[4]
      + a[5]*a[5]
      + a[6]*a[6]
      + a[7]*a[7]
      + a[8]*a[8]
    )
  }
docs: Returns Frobenius norm of a mat3
  
  @alias mat3.frob
  @param {mat3} a the matrix to calculate Frobenius norm of
  @returns {Number} Frobenius norm