“…In the past few decades, many authors have been devoted to study the number of limit cycles of piecewise smooth differential systems with two zones separated by a switching line, see [3,4,7,9,13,15,17,21,22,25,27] and the references quoted therein. The ways used in the aforementioned works are Melnikov function established in [8,17] and averaging method developed in [18,19]. Recently, Yang and Zhao [28] used the Picard-Fuchs equation to calculate the first order Melnikov function of a kind of piecewise smooth differential systems with a switching line, which can reduce a lot of calculation work.…”