docs: public static boolean isIdentity(DMatrixRMaj mat , double tol )
      {
          // see if the result is an identity matrix
          int index = 0;
          for( int i = 0; i < mat.numRows; i++ ) {
              for( int j = 0; j < mat.numCols; j++ ) {
                  if( i == j ) {
                      if( !(Math.abs(mat.get(index++)-1) <= tol) )
                          return false;
                  } else {
                      if( !(Math.abs(mat.get(index++)) <= tol) )
                          return false;
                  }
              }
          }
  
          return true;
      }