matlab 如何把一维数组扩展为重复的三维数组

a=[1 2 3]
b=[a(1) a(1) a(1); a(1) a(1) a(1);a(2) a(2) a(2);a(2) a(2) a(2);a(3) a(3) a(3);a(3) a(3) a(3)]