matlab 各种函数详解（收集）

unique函数格式 b= unique (a) %取集合a的不重复元素构成的向量b = unique (A,'rows') %返回A、B不同行元素组成的矩阵[b,i,j] = unique (…) %i体现b中元素在原向量（矩阵a）中的位置；j体现原向量（矩阵a）在b中的位置例1-39>> A=[1 1 2 2 4 4 6 4 6]A =1 1 2 2 4 4 6 4 6>> [c,i,j]=unique(A)c =1 2 4 6i =2 4 8 9 %i体现b中元素在原向量（矩阵a）中的位置；j =1 1 2 2 3 3 4 3 4 %j体现原向量（矩阵a）在b中的位置例1-40>> A=[1 2 2 4;1 1 4 6;1 1 4 6]A =1 2 2 41 1 4 61 1 4 6>> [c,i,j]=unique(A,'rows')c =1 1 4 61 2 2 4i =31j =211

find -Find indices and values of nonzero elements

Syntax

ind = find(X)ind = find(X, k)ind = find(X, k, 'first')ind = find(X, k, 'last')[row,col] = find(X, ...)[row,col,v] = find(X, ...)

Description

ind = find(X) locates all nonzero elements of array X,and returns the linear indices of those elements in vector ind.If X is a row vector, then ind is a row vector; otherwise, ind isa column vector. If X contains no nonzero elements or is an empty array, then ind is an empty array.ind = find(X, k) or ind= find(X, k, 'first') returns at most the first k indices corresponding to the nonzero entries of X. k mustbe a positive integer, but it can be of any numeric data type.ind = find(X, k, 'last') returns at most the last k indicescorresponding to the nonzero entries of X.[row,col] = find(X, ...) returns the row and column indices of the nonzero entries in thematrix X. This syntax is especially useful when working with sparse matrices. If X is an N-dimensional array withN > 2, col contains linear indices for the columns. For example, for a 5-by-7-by-3 array X with a nonzero elementatX(4,2,3), find returns 4 in row and16 in col. That is, (7 columns in page 1) + (7 columns in page 2) + (2 columns in page 3) = 16.[row,col,v] = find(X, ...) returns a column or row vector v ofthe nonzero entries in X, as well as row and column indices. If X is a logical expression, then v isa logical array. Output v contains the non-zero elements of the logical array obtained by evaluating the expression X.For example,

A= magic(4)
A =
16     2     3    13
5    11    10     8
9     7     6    12
4    14    15     1

[r,c,v]= find(A>10);

r', c', v'
ans =
1     2     4     4     1     3
ans =
1     2     2     3     4     4
ans =
1     1     1     1     1     1

Here the returned vector v is a logical array that contains the nonzero elements of N where

N=(A>10)

Examples

Example 1

X = [1 0 4 -3 0 0 0 8 6];
indices = find(X)

returns linear indices for the nonzero entries of X.

indices =
1     3     4     8     9

Example 2

You can use a logical expression to define X. For example,

find(X > 2)

returns linear indices corresponding to the entries of X that are greater than 2.

ans =
3     8     9

Example 3

The following find command

X = [3 2 0; -5 0 7; 0 0 1];
[r,c,v] = find(X)

returns a vector of row indices of the nonzero entries of X

r =
1
2
1
2
3

a vector of column indices of the nonzero entries of X

c =
1
1
2
3
3

and a vector containing the nonzero entries of X.

v =
3
-5
2
7
1

Example 4

The expression

X = [3 2 0; -5 0 7; 0 0 1];
[r,c,v] = find(X>2)

returns a vector of row indices of the nonzero entries of N where N=(X>2)

r =
1
2

a vector of column indices of the nonzero entries of N where N=(X>2)

c =
1
3

and a logical array that contains the nonzero elements of N where N=(X>2).

v =
1
1

Recall that when you use find on a logical expression, the output vector v does not contain the nonzero entriesof the input array. Instead, it contains the nonzero values returned after evaluating the logical expression.

Example 5

Some operations on a vector

x = [11  0  33  0  55]';

find(x)
ans =
1
3
5

find(x == 0)
ans =
2
4

find(0 < x & x < 10*pi)
ans =
1

Example 6

For the matrix

M = magic(3)
M =
8     1     6
3     5     7
4     9     2

find(M > 3, 4)

returns the indices of the first four entries of M that are greater than 3.

ans =
1
3
5
6

Example 7

If X is a vector of all zeros, find(X) returns an empty matrix. For example,

indices = find([0;0;0])
indices =
Empty matrix: 0-by-1

isnan函数

[功能描述]          判断数组中的元素是否为无穷大
[函数描述]          tf=isnan(A)：返回一个与A相同维数的数组，若A的元素为NaN（非数值），在对应位置上返回逻辑1（真），否则返回逻辑0（假）。对虚数z，如果z的实部或虚部都是NaN，那么isnan函数返回逻辑1，如果实部和虚部都是inf，则返回逻辑0。
eye函数
Y = eye(n) 返回n乘n单一矩阵

Y = eye(m,n) or eye([m n]) 对角线是1，其他是0。

Y = eye(size(A)) 返回统一大小的单一矩阵

堆叠矩阵repmat

使用用法如下：B = repmat(A,m,n)B = repmat(A,[m n])B = repmat(A,[m n p...])这是一个处理大矩阵且内容有重复时使用，其功能是以A的内容堆叠在（MxN）的矩阵B中，B矩阵的大小由MxN及A矩阵的内容决定，如果A是一个3x4x5的矩阵，有B = repmat(A,2,3)则最后的矩阵是6x12x5例如：>>B=repmat( [1 2;3 4],2,3)B = 1 2 1 2 1 23 4 3 4 3 41 2 1 2 1 23 4 3 4 3 4其结果变为4X6。Ａ也可以置放文字串，如：>>C=repmat(' Long live the king!', 2,2)C =Long live the king! Long live the king!Long live the king! Long live the king!也可置放其他的：>> D=repmat(NaN,2,5)D =NaN NaN NaN NaN NaNNaN NaN NaN NaN NaN