docs: public static void setIdentity( ZMatrixRMaj mat )
      {
          int width = mat.numRows < mat.numCols ? mat.numRows : mat.numCols;
  
          Arrays.fill(mat.data,0,mat.getDataLength(),0);
  
          int index = 0;
          int stride = mat.getRowStride();
  
          for( int i = 0; i < width; i++ , index += stride + 2) {
              mat.data[index] = 1;
          }
      }