How to create a Mat (1D) with sequential values?

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no, no such thing built in.

you simply set up your Mat, and fill it with numbers, manually:

Mat m(1,10,CV_64F); // 10 doubles in a single row
for (int i=0; i<10; i++)
      m.at<double>(0,i) = i; // set the column in row 0

note, that there are notorious differences between c++ and matlab, like 0 or 1 based indexing, so careful !