matlab 一些命令
>> 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
>>
