Access multiple channels in Mat

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What is the Syntax to access ith row of channel::n of a multi channel matrix. I can access (i,j) element of channel::n but what is the syntax to use functions like row, rowRange, .....

Sample Code:

Mat M(10, 3, CV_32SC3);
cout << M.at<Vec3d>(0,0)[1] << endl;  // This works
cout << M.row(0)[1] << endl;    // Syntax of this