变量积分用int比较好
>> help int
--- help for sym/int.m ---
INT Integrate.
INT(S) is the indefinite integral of S with respect to its symbolic
variable as defined by FINDSYM. S is a SYM (matrix or scalar).
If S is a constant, the integral is with respect to 'x'.
INT(S,v) is the indefinite integral of S with respect to v. v is a
scalar SYM.
INT(S,a,b) is the definite integral of S with respect to its
symbolic variable from a to b. a and b are each double or
symbolic scalars.
INT(S,v,a,b) is the definite integral of S with respect to v
from a to b.
--------------------------------------------------------------------
