>> help nextpowe2

nextpowe2.m not found.

Use the Help browser Search tab to search the documentation, or
type "help help" for help command options, such as help for methods.

>>  help nextpow2
NEXTPOW2 Next higher power of 2.
    NEXTPOW2(N) returns the first P such that 2^P >= abs(N).  It is
    often useful for finding the nearest power of two sequence
    length for FFT operations.
    NEXTPOW2(X), if X is a vector, is the same as NEXTPOW2(LENGTH(X)).
    Class support for input N or X:
       float: double, single
    See also log2, pow2.

    Reference page in Help browser
       doc nextpow2

>> help max
MAX    Largest component.
    For vectors, MAX(X) is the largest element in X. For matrices,
    MAX(X) is a row vector containing the maximum element from each
    column. For N-D arrays, MAX(X) operates along the first
    non-singleton dimension.
    [Y,I] = MAX(X) returns the indices of the maximum values in vector I.
    If the values along the first non-singleton dimension contain more
    than one maximal element, the index of the first one is returned.
    MAX(X,Y) returns an array the same size as X and Y with the
    largest elements taken from X or Y.  Either one can be a scalar.
    [Y,I] = MAX(X,[],DIM) operates along the dimension DIM.
    When complex, the magnitude MAX(ABS(X)) is used, and the angle
    ANGLE(X) is ignored.  NaN\'s are ignored when computing the maximum.
    Example: If X = [2 8 4   then max(X,[],1) is [7 8 9],
                     7 3 9]
        max(X,[],2) is [8    and max(X,5) is [5 8 5
                        9],                   7 5 9].
    See also min, median, mean, sort.

    Overloaded functions or methods (ones with the same name in other directories)
       help timeseries/max.m
       help quantizer/max.m
       help fints/max.m
       help localpoly/max.m
       help localpspline/max.m

    Reference page in Help browser
       doc max

>>

nargin是用来判断输入变量个数的函数，这样就可以针对不同的情况执行不同的功能。通常可以用他来设定一些默认值，如下面的函数。

例子，函数test1的功能是输出a和b的和。如果只输入一个变量，则认为另一个变量为0，如果两个变量都没有输入，则默认两者均为0。

function y=test1(a,b)
if nargin==0
    a=0;b=0;
elseif nargin==1
    b=0;
end
y=a+b;

>> i=imread(\'mars.jpg\');
>> size(i)

ans =

        1055        1200

>>

>> [PQ,n]=paddedsize(size(i));
>> n

n =

     1

>>

>> [PQ,n]=paddedsize(size(i));
>> n

n =

     1

>> PQ

PQ =

        2110        2400

>> size(i)

ans =

        1055        1200

>>

源代码:

function [PQ,n]=paddedsize(AB,CD,PARAM)
%
n=nargin;
if nargin==1
    PQ=2*AB;
elseif nargin==2 & ~ischar(CD);
    PQ=AB+CD-1;
    PQ=2*ceil(  PQ/2);
elseif nargin==2
    m=max(AB);
   P=2^nextpow2(2*m);
   P=[P,P];
elseif nargin==3
    m=max([AB,CD]);
    P=2^nextpow2(2*m);
    PQ=[P,P];
else
    error(\'wrong number of inputs\')
end

>> [PQ,n]=paddedsize(size(i),size(i));
>> n

n =

     2

>> PQ

PQ =

        2110        2400

>>

>> [PQ,n]=paddedsize(size(i),size(i));
>> n

n =

     2

>> PQ

PQ =

        2110        2400

>> [PQ,n]=paddedsize(size(i),size(i));
>> n

n =

     2

>> PQ

PQ =

        2110        2400

>> m=max(size(i));
>> M

M =

     8

>>  P=2^nextpow2(2*m);
>> P

P =

        4096

>> U=nextpow2(2*m);
>> U

U =

    12

>>  PQ=[P,P];
>> PQ

PQ =

        4096        4096

>> ~ischar(size(i))

ans =

     1

>> PQ=size(i)+size(i)-1

PQ =

        2109        2399

>> PQ=2*ceil(  PQ/2);
>> PQ

PQ =

        2110        2400

>>