The program title almost tells the whole story. Along with Copland’s Symphony No. 3 and Rachmaninoff’s Piano Concerto No. 1—Olga Kern at the keyboard—a number of symphony orchestras, including the NSO, have each commissioned a variation on Paganini’s Caprice No. 24. It’s their birthday gift to Maestro Slatkin, an addendum to the set of variations he commissioned while leading the St. Louis Symphony Orchestra. The new work is called Yet Another Set of Variations (on a Theme of Paganini). —L.J.