floor：朝负无穷方向舍入
B = floor(A) rounds the elements of A to the nearest integers less than or equal to A.
ceil：朝正无穷方向舍入
B = ceil(A) rounds the elements of A to the nearest integers greater than or equal to A.
fix：朝零方向舍入
B = fix(A) rounds the elements of A toward zero, resulting in an array of integers.
round：四舍五入
B = round(A) rounds the elements of X to the nearest integers.
Example：
a= [-0.9, -2.1, -0.4, 0.3, 0.8, 1.1, 2.7, -1.2+2.9i];
floor(a)=[ -1, -3, -1, 0, 0, 1, 2, -2+2i]
ceil(a)= [ 0, -2, 0, 1, 1, 2, 3, -1+3i]
fix(a)= [ 0, -2, 0, 0, 0, 1, 2, -1+2i]
round(a)=[-1, -2, 0, 0, 1, 1, 3, -1+3i]
注：For complex X, for all the four fuctions the imaginary and real parts are rounded independently.