From the book:

“The Tuxedo Jacket, knit from top to bottom, is shaped like a trapezoid and is knit in a stretchy rib stitch. By folding the two sides up, the jacket has a short front with diagonal ribs and a long back with vertical ribs. Increasing by four stitches simultaneously fans out the rib at the center back. Knit the front and back as one piece and then pick up stitches to complete the sleeves.”

Tuxedo Jacket Adaptation using Cascade Magnum through the LA Times