matlab中mod（）函数究竟有什么用？具体的作用（不要告诉我怎么算，我只想知道他有什么用）

数学函数取模。。。
如5mod3=2 其实就是取余

看 Help Mod

help mod
MOD Modulus after division.
MOD(x,y) is x - n.*y where n = floor(x./y) if y ~= 0. If y is not an
integer and the quotient x./y is within roundoff error of an integer,
then n is that integer. The inputs x and y must be real arrays of the
same size, or real scalars.

The statement "x and y are congruent mod m" means mod(x,m) == mod(y,m).

By convention:
MOD(x,0) is x.
MOD(x,x) is 0.
MOD(x,y), for x~=y and y~=0, has the same sign as y.

Note: REM(x,y), for x~=y and y~=0, has the same sign as x.
MOD(x,y) and REM(x,y) are equal if x and y have the same sign, but
differ by y if x and y have different signs.

See also rem.

Overloaded methods:
codistributed/mod
sym/mod

Reference page in Help browser
doc mod