docs: public static void setIdentity( DMatrix1Row mat )
      {
          int width = mat.numRows < mat.numCols ? mat.numRows : mat.numCols;
  
          Arrays.fill(mat.data,0,mat.getNumElements(),0);
  
          int index = 0;
          for( int i = 0; i < width; i++ , index += mat.numCols + 1) {
              mat.data[index] = 1;
          }
      }