2022年Matlab知識(shí)歸納總結(jié)

1、Matlab 筆記 基礎(chǔ)操作 1,基礎(chǔ)命令 Cd+確定路徑 ：轉(zhuǎn)變當(dāng)前目錄 Pwd ：查看當(dāng)前目錄的確定路徑 doc addpath：顯現(xiàn)幫忙菜 單中關(guān)于 addpath 的學(xué)問(wèn) help addpath ：命令窗口顯現(xiàn) addpath 的介紹 lookfor ：關(guān)鍵詞搜尋命令, lookfor color 與 color 有關(guān)的函數(shù) 注：搜尋時(shí)有時(shí)會(huì)顯現(xiàn)大量信息,按 ctrl+C 可終止搜尋,或者在使用該命令 前先輸入 more on 來(lái)啟動(dòng)分屏顯示功能,輸入 more off 回車(chē),可以關(guān)閉分屏顯 示功能； What : ：查看當(dāng)前目錄下的文件那些和 matlab 有關(guān) What gene

2、ral：列出 matlab 的基礎(chǔ)函數(shù)名 WhichDemo：可以很便利地給出某個(gè)函數(shù)的確定路徑 ：可以進(jìn)入 matlab 自帶的演示教程 回車(chē) home 回車(chē) 將光標(biāo)置于當(dāng)前窗口的左上方 1Edit Edit or create file Alternatives As an alternative to the edit function, select File New or Open in the MATLAB desktop or any desktop tool. Syntax edit edit edit edit fun1 fun2 fun3 . edit classname/

3、fun edit private/fun edit classname/private/fun edit +packagename/classname/fun editmy file.m Description edit opens a new editor window. filespecification can include a partial path, complete path, relative path, or no path. Be aware of the following: If you do not specify a path, the current folde

4、r is the default. If you specify a path, the folder must exist; otherwise MATLAB returns an error. If you specify a path and the folder exits, but the specified file does not, a prompt opens such as shown in the following image: To create a blank file named fun.m in the specified folder, click Yes.

5、To suppress the prompt, select Donot show this prompt again. To reinstate 第 1 頁(yè),共 88 頁(yè)the prompt after suppressing it, open the Preferences dialog box by selecting File Preferences General Confirmation Dialogs and then selecting Prompt when editing files that do not exist in the pane on the right. e

6、dit file.ext opens the specified file. edit fun1 fun2 fun3 . opens fun1.m, fun2.m, fun3.m, and so on, in the default editor. edit classname/fun, or edit private/fun, or edit classname/private/fun opens a method, private function, or private method for the namedclass. edit +packagename/classname/fun

7、opens a method for the namedclass in the named package. editmy file.m opens the file my file.m in the default editor. This form of the edit function is useful when a file name contains a space; you cannot use the command form in such a case. 2,命令輸入的幾個(gè)有用方法 a,利用 tab 按鍵 輸入命令的前幾個(gè)字符,接著連按兩下 tab 鍵,顯現(xiàn)函數(shù)列表 b

8、,利用鍵盤(pán)上的上下方向鍵,調(diào)出歷史命令 c,當(dāng) matlab 按次序執(zhí)行很多命令時(shí),可將要運(yùn)行的大量命令統(tǒng)一存放在一個(gè)文本文件里, 擴(kuò)展名為 .m,然后在命令窗口鍵入這個(gè)文件名,回車(chē), 3,matlab 保留常數(shù) Ans eps ：當(dāng)前運(yùn)算機(jī)的零閾值 matlab 就會(huì)一次性地執(zhí)行這些命令 i 和 f ：如 i 和 f 值不被改寫(xiě), 就它們代表虛數(shù)單位, 使用前, 應(yīng)確定它們沒(méi)有被改寫(xiě)； 復(fù)原變量： i=sqrt （-1）； Inf ：無(wú)窮大,負(fù)無(wú)窮用 -inf 表示 NaN：非數(shù)（ not a number ） Nargin：函數(shù)輸入的變量的實(shí)際個(gè)數(shù) Nargout ：函數(shù)輸出變量的實(shí)際個(gè)數(shù)

9、 Pi ：圓周率 4,變量命名規(guī)章 首個(gè)字符必需是字母,并且后面字符不能包含空格,標(biāo)點(diǎn)和括號(hào)； Matlab 中大小寫(xiě)字符 表示的含義不同 5,數(shù)據(jù)類(lèi)型結(jié)構(gòu) 利用 help datatype 查看全部的數(shù)據(jù)類(lèi)型基本類(lèi)型 常用的： 數(shù)值型：雙精度,浮點(diǎn)數(shù),其 matlab 表示為 double 規(guī)律型：只包含 1,0 ； 1 為 true , 0 為 false 字符型：賦值時(shí),字符串是用單引號(hào)括起來(lái)的 單元數(shù)據(jù) clear all % 清除運(yùn)算機(jī)內(nèi)存所儲(chǔ)存的變量和函數(shù) who % 查看當(dāng)前內(nèi)存里的變量名 whos % 查看當(dāng)前內(nèi)存里變量的詳細(xì)說(shuō)明 clc % 清屏 注：命令行結(jié)尾加上一個(gè)分號(hào)表

10、示不屏顯結(jié)果,只運(yùn)行命令； 第 2 頁(yè),共 88 頁(yè)矩陣 1, 基本規(guī)章 a, 矩陣元素必需在中括號(hào)內(nèi) b, 同行元素之間用空格或逗號(hào)隔開(kāi) c, 行與行之間可以用分號(hào)或回車(chē)隔開(kāi) d, 假如矩陣的某行過(guò)長(zhǎng),可以在續(xù)行符 后另起一行接著輸入 2, 矩陣函數(shù) Ones ：生成元素全為 1 的矩陣, onesn 將生成 n*n 的矩陣 Zeros ：生成元素全為 0 的矩陣 Nan ：生成元素全為 nan 的矩陣 區(qū)間均勻Rand ：生成在 0,1 分布的隨機(jī)矩陣 Randn ：生成均值為 0,方差為 1 的標(biāo)注正態(tài)分布隨機(jī)矩陣 Eye ：生成單位矩陣,主對(duì)角線元素全為 1Linspace ：生成等間

11、隔的行向量,其調(diào)用格式為： linspacea,b,n ,其中 a 和 b 是生成 向量的第一個(gè)和最終一個(gè)元素, n 是元素總數(shù) Magic ：魔方矩陣 3,矩陣運(yùn)算 + - * / 右除 左除 乘方 轉(zhuǎn)置 a,點(diǎn)運(yùn)算 點(diǎn)運(yùn)算符號(hào)有 .* ./ . . 兩矩陣進(jìn)行點(diǎn)運(yùn)算是指對(duì)它們的對(duì)應(yīng)元素進(jìn)行相關(guān)運(yùn)算,要求兩個(gè)矩陣的維數(shù)相同 b,關(guān)系運(yùn)算 = b=-3:2 % 生成間隔為 1 的向量 c=130:-2.4:115 % 中間可以指定任意間隔 d=a:,3 % 提取矩陣 a 的第 3 列元素,并轉(zhuǎn)置后賦值給變量 dE,矩陣的維數(shù) a= 1 2 3 4 7 8 9 10 3 4 6 9 5 7 10

12、 11 s1,s2=sizea %將矩陣 a 的每一維的長(zhǎng)度賦值給 s1 和 s2 S1=4 s2=4 向量 b 的長(zhǎng)度 b=-3 -2 -1 0 1 2 b1=lengthb %第 3 頁(yè),共 88 頁(yè)b1= 6 ndimsa%直接得到 a 的維數(shù) Ans=2 f ,空矩陣的應(yīng)用 空矩陣的表示 a3,:= %刪除矩陣 a 的第 3 行 h,矩陣的翻轉(zhuǎn) 1 利用撇號(hào)可以實(shí)現(xiàn)矩陣的行列互換 2fliplra % 將矩陣 a 左右翻轉(zhuǎn),第一列變成最終一列,以此類(lèi)推 flipuda % 將矩陣 a 上下翻轉(zhuǎn),第一行變成最終一行,以此類(lèi)推 rot90a % 將矩陣 a 逆時(shí)針旋轉(zhuǎn) 90 度 Rot90

13、a,k : 將矩陣 a 逆時(shí)針旋轉(zhuǎn) k 倍的 90 度, k 為 1 可省略 g,矩陣的拼接 b=a ones3,6*2;nansizea a-1 k,基本函數(shù)操作 help elfun 和 help matfun 可以查看基本的數(shù)學(xué)函數(shù)和線性代數(shù)運(yùn)算函數(shù)列表 suma % 對(duì)矩陣 a 的每一列求和 suma:; % 對(duì)矩陣 a 的全部元素求和 a: 將矩陣 a 變成向量 a 補(bǔ)充： type + 文件名 % 查看當(dāng)期文件目錄下的內(nèi)容 利用 mat 文件可以將當(dāng)前 matlab 工作空間中的一些有用的變量長(zhǎng)期地保留下來(lái),擴(kuò)展名 為.mat , mat 文件生成和裝入用 save 和 load

14、命令完成 常用格式： Save 文件名 變量名表 -append-ascii load 文件名 變量名表 -ascii save wps % 儲(chǔ)存為 文件 lsload wps %裝入 mat 文件 save wps x y %只儲(chǔ)存 x y 變量 load wps x %只裝入 x 變量 help tic/toc %時(shí)間機(jī)器 取整函數(shù) : fix floor ceil round fix1.2=1 fix2.3=2 靠近 0 取整 floor1.2=1floor-1.2=2 靠近負(fù)無(wú)窮取整 ceil1.2=2 ceil-1.2=-1 靠近正無(wú)窮取整 round1.2=1 round1.6=2

15、 四舍五入 a= 1 2 3;4 5 6 aend,end ans=6 aend-1,endans=2 Matlab 指令及函數(shù)總結(jié) 第 4 頁(yè),共 88 頁(yè)logical Convert numeric values to logical Syntax K = logicalA K = logicalA returns an array that can be used for logical indexing or logical tests. Examples the statement B = logicaleye3 returns Given A = 1 2 3; 4 5 6; 7

16、8 9, a logical array B = 100indexing that returns As diagonal elements: 010001which can be used in logical AB ans = 1 5 9 However, attempting to index into A using the numeric array eye3 results in: Aeye3 . Subscript indices must either be real positive integers or logicals. ndims Number of array di

17、mensions Syntax n = ndimsA Description n = ndimsA returns the number of dimensions in the array A. The number of dimensions in an array is always greater than or equal to 2. Trailing singleton dimensions are ignored. A singleton dimension is any dimension for which sizeA,dim = 1. Algorithms ndimsx i

18、s lengthsizex. size Array dimensions Syntax d = sizeX m,n = sizeX m = sizeX,dim d1,d2,d3,.,dn = sizeX, Description 第 5 頁(yè),共 88 頁(yè)d = sizeX returns the sizes of each dimension of array X in a vector d with ndimsX elements. If X is a scalar, which MATLABsoftware regards as a 1-by-1 array, sizeX returns

19、the vector 1 1. m,n = sizeX returns the size of matrix X in separate variables m and n. m= sizeX,dim returns the size of the dimension of X specified by scalar dim.d1,d2,d3,.,dn = sizeX, for n 1, returns the sizes of the dimensions of the array X in the variables d1,d2,d3,.,dn, provided the number o

20、f output arguments n equals ndimsX. If n does not equal ndimsX, the following exceptions hold: n ndimsX size returns ones in the extra variables, that is, those corresponding to ndimsX+1 through n. Examples Example 1 The size of the second dimension of rand2,3,4 is 3. m = sizerand2,3,4,2 m = 3 Here

21、the size is output as a single vector. d = sizerand2,3,4 d = 234Here the size of each dimension is assigned to a separate variable. m,n,p = sizerand2,3,4 m = 2n = 3p = 4 Example 2 If X = ones3,4,5, then d1,d2,d3 = sizeX d1 = d2 = d3 = 第 6 頁(yè),共 88 頁(yè)3 4 5But when the number of output variables is less

22、than ndimsX: d1,d2 = sizeX d1 = d2 = 3 20 The extra dimensions are collapsed into a single product. If n ndimsX, the extra variables all represent singleton dimensions: d1,d2,d3,d4,d5,d6 = sizeX d1 = d2 = d3 = 5d6 = 134d4 = d5 = 1length 1Length of vector or largest array dimension Syntax numberOfEle

23、ments = lengtharray Description numberOfElements = lengtharray finds the number of elements along the largest dimension of an array. array is an array of any MATLAB data type and any valid dimensions. numberOfElements is a whole number of the MATLAB double class. For nonempty arrays, numberOfElement

24、s is equivalent to maxsizearray. For empty arrays, numberOfElements is zero. Examples Create a 1-by-8 array X and use length to find the number of elements inthe second largest dimension: X = 5, 3.4, 72, 28/4, 3.61, 17 94 89; lengthX ans = 8Create a 4-dimensional array Y in which the third dimension

25、 is the largest. Use length to find the number of elements in that dimension: Y = rand2, 5, 17, 13; lengthY ans = 17 第 7 頁(yè),共 88 頁(yè)Create a struct array S with character and numeric fields of different lengths. Use the structfun function to apply length to each field of S: S = structf1, Name:, f2, Cha

26、rlie, . f3, DOB:, f4, 1917 S = f1: Name: f2: Charlief3: DOB: f4: 1917 structfunfieldlengthfield, S ans = 5741numel Number of elements in array or subscripted array expressionSyntax n = numelA n = numelA, index1, index2, . indexn Description n = numelA returns the number of elements, n, in array A. n

27、 = numelA, index1, index2, . indexn returns the number of subscripted elements, n, in Aindex1, index2, ., indexn. To handle the variable number of arguments, numel is typically written with the header function n = numelA, varargin, where varargin is a cell array with elements index1, index2, . index

28、n. The MATLABsoftware implicitly calls the numel built-in function whenever an expression generates a comma-separated list. This includes brace indexing i.e., Aindex1,index2,.,indexN, and dot indexing i.e., A.fieldname.Tips It is important to note the significance of numel with regards to the overlo

29、aded subsref and subsasgn functions. In the case of the overloaded subsref function for brace and dot indexing as described in the last paragraph, numel is used to compute the number of expected outputs nargout returned from subsref. For the overloaded subsasgn function, numel is used to compute the

30、 number of expected inputs nargin to be assigned using subsasgn. The nargin value for the overloaded subsasgn function is the value returned by numel plus 2 one for the variable being assigned to, and one for the structure array of subscripts. As a class designer, you must ensure that the value of n

31、 returned by the 第 8 頁(yè),共 88 頁(yè)built-in numel function is consistent with the class design for that object. If n is different from either the nargout for the overloaded subsref function or the nargin for the overloaded subsasgn function, then you need to overload numel to return a value of n that is c

32、onsistent with the class subsref and subsasgn functions. Otherwise, MATLAB produces errors when calling these functions. Examples Create a 4-by-4-by-2 matrix. numel counts 32 elements in the matrix. a = magic4; a:,:,2 = a a:,:,1 = 16 2313 511 10 897612 414 15 1a:,:,2 = 16 594211 714 310 615 13 812 1

33、numela ans = 32 reshapeReshape arraySyntax B = reshapeA,m,n B = reshapeA,m,n,p,. B = reshapeA,m n p . B = reshapeA,.,. B = reshapeA,siz Description B = reshapeA,m,n returns the m-by- n matrix B whose elements are taken column-wise from A. An error results if A does not have m*n elements. B = reshape

34、A,m,n,p,. or B = reshapeA,m array with the same elements as A n p . returns an n-dimensional but reshaped to have the size m-by- n-by- p-by- . . The product of the specified dimensions, m*n*p* ., must be the same as prodsizeA . B = reshapeA,.,. calculates the length of the dimension represented by t

35、he placeholder , such that the product of the dimensions equals prodsizeA . The value of prodsizeA must be evenly divisible by the 第 9 頁(yè),共 88 頁(yè)product of the specified dimensions. You can use only one occurrence of . . B = reshapeA,siz returns an n-dimensional array with the same elements as A, but

36、reshaped to siz , a vector representing the dimensions of the reshaped array. The quantity prodsiz must be the same as prodsizeA Examples Reshape a 3-by- 4matrix into a 2 -by- 6 matrix. A = 10 14725811 36912 B = reshapeA,2,6 B = 1357911 12 246810 B = reshapeA,2, B = 1357911 246810 12 permute Rearran

37、ge dimensions of N-D arraySyntax B = permuteA,order Description B = permuteA,order rearranges the dimensions of A so that they are in the order specified by the vector order . B has the same values of A but the order of the subscripts needed to access any particular element is rearranged as specifie

38、d by order . All the elements of order must be unique. Tips permute and ipermute are a generalization of transpose . for multidimensional arrays. Examples Given any matrix A, the statement permuteA,2 1 is the same asA. . For example: A = 1 2; 3 4; permuteA,2 1 ans = 1 32 4The following code permutes

39、 a three-dimensional array: 第 10 頁(yè),共 88 頁(yè)X = rand12,13,14; Y = permuteX,2 3 1; sizeY ans = 13 14 12 repmat Replicate and tile arraySyntax B = repmatA,m,n B = repmatA,m n B = repmatA,m n p. Description B = repmatA,m,n creates a large matrix B consisting of an m-by- n tiling of copies of A. The size o

40、f B is sizeA,1*m , sizeA,2*n . The statement repmatA,n creates an n-by- n tiling. B = repmatA,m n accomplishes the same result as repmatA,m,n . B = repmatA,m n p. produces a multidimensional array B composed of copies of A. The size of B is sizeA,1*m , sizeA,2*n , sizeA,3*p , . . Tips repmatA,m,n ,

41、when A is a scalar, produces an m-by- n matrix filled with As value and having As class . For certain values, you can achieve the same results using other functions, as shown by the following examples: repmatNaN,m,n returns the same result as NaNm,n . . . repmatsingleinf,m,n is the same as infm,n,si

42、ngle repmatint80,m,nis the same as zerosm,n,int8 . repmatuint321,m,n is the same as onesm,n,uint32 repmateps,m,n is the same as epsonesm,n . ExamplesExample 1 In this example, repmat replicates 12 copies of the second-order identity matrix, resulting in a checkerboard pattern. B = repmateye2,3,4 B =

43、 1 0 1 0 1 0 1 00 1 0 1 0 1 0 11 0 1 0 1 0 1 00 1 0 1 0 1 0 11 0 1 0 1 0 1 00 1 0 1 0 1 0 1The statement N = repmatNaN,2 3 creates a 2-by- 3 matrix of NaNs. Example 2 If you have code that uses repmat and also a binary operator or function, you can transform the code to use the bsxfun function inste

44、ad. In certain 第 11 頁(yè),共 88 頁(yè)cases, this can provide a simpler and faster solution. This example replaces the sumof two repmat operations with a single call to bsxfun : x = 1:5; y = 1:10; % Replace this code repmatx,10,1 + repmaty,1,5 % with the following: bsxfunplus, x, y find Find indices and value

45、s of nonzero elementsSyntax ind = findXind = findX, k ind = findX, k, first ind = findX, k, last row,col = findX, . row,col,v = findX, . Description ind = findX locates all nonzero elementsindices of those elements in vector indof array X, and returns the linear . If X is a row vector, then ind is a

46、 row vector; otherwise, ind is a column vector. If X contains no nonzero elements or is an empty array, then ind is an empty array. ind = findX, k or ind = findX, k, first returns at most the first k indices corresponding to the nonzero entries of X. k must be a positive integer, but it can be of an

47、y numeric data type. ind = findX, k, last returns at most the last k indices corresponding col to the nonzero entries of X. row,col = findX, . returns the row and column indices of the nonzero entries in the matrix X. This syntax is especially useful when working with sparse matrices. If X is an N-d

48、imensional array with N 2, contains linear indices for the columns. For example, for a 5-by-7-by-3 array X with a nonzero element at X4,2,3 , find returns 4 in row and 16 in col . That is, 7 columns in page 1 + 7 columns in page 2 + 2 columns in page 3 = 16. row,col,v = findX, . returns a column or

49、row vector v of the nonzero entries in X, as well as row and column indices. If X is a logical expression, then v is a logical array. Output v contains the non-zero elements of the logical array obtained by evaluating the expression X. For example,A= magic4A = 16 2313 第 12 頁(yè),共 88 頁(yè)511 10 897612 414

50、15 1r,c,v= findA10; r, c, v ans = 124413ans = 122344v is a logical array that contains the nonzero ans = 111111Here the returned vector elements of N where N=A10 Examples Example 1 X = 1 0 4 -3 0 0 0 8 6; indices = findX returns linear indices for the nonzero entries of indices = X. 13489Example 2 Y

51、ou can use a logical expression to define findX 2 X. For example, returns linear indices corresponding to the entries of X that are greater than 2. ans = 389Example 3 The following find command X = 3 2 0; -5 0 7; 0 0 1; r,c,v = findX returns a vector of row indices of the nonzero entries of X r = 1

52、2 12 3 a vector of column indices of the nonzero entries of X c = 1第 13 頁(yè),共 88 頁(yè)1 23 3and a vector containing the nonzero entries of v = X. 3-5 27 1 Example 4 The expression X = 3 2 0; -5 0 7; 0 0 1; r,c,v = findX2 returns a vector of row indices of the nonzero entries of N where N=X2 r = 1 2a vecto

53、r of column indices of the nonzero entries of c = 1 3N where N=X2 and a logical v = array that contains the nonzero elements of N where N=X2 . 1 1Recall that when you use find on a logical expression, the output vector v does not contain the nonzero entries of the input array. Instead, it contains t

54、he nonzero values returned after evaluating the logical expression. Example 5 Some operations on a vector x = 11 0 33 0 55; findx ans = 135findx = 0 ans = 2第 14 頁(yè),共 88 頁(yè)4find0 x & x 3, 4 returns the indices of the first four entries of 3. ans = 1 3 5 6 Example 7 Mthat are greater than If X is a vect

55、or of all zeros, findX returns an empty matrix. For example, indices = find0;0;0 indices = Empty matrix: 0-by-1 cell Create cell array Syntax C = celldim C = celldim1,.,dimN D = cellobj Description C = celldim creates a cell array of empty matrices. If dim is a scalar, C is dim-by-dim. If dim is a v

56、ector, C is dim1-by-.-dimN, where N is the number of elements of dim. C= celldim1,.,dimN creates cell array C, where Cis dim1-by-.-dimN. or System.Object into a MATLAB cell array. Tips Creating an empty array with the cell function, such as C = cell3,4,2; is exactly equivalent to assigning an empty

57、array to the last index of a new cell array: 第 15 頁(yè),共 88 頁(yè)C3,4,2 = ; Input Arguments dim Scalar integer or vector of integers that specifies the dimensions of cell array C. dim1,.,dimN obj Scalar integers that specify the dimensions of C. One of the following: Java array or object .NET array of type

58、 System.String or Output Arguments C Cell array. Each cell contains an empty, 0-by-0 array of type double. D Cell array. Each cell contains a MATLAB type closest to the Java or .NET type. For more information, see: Conversion of Java Return Types .NET Type to MATLAB Type Mapping Examples Create an e

59、mpty 3-by-4-by-2 cell array. mycell = cell3,4,2; Create a cell array that is the samesize as mycell, created in the previous example. similar = cellsizemycell; Convert an array of java.lang.String objects into a MATLAB cell array. strArray = java_arrayjava.lang.String, 3; strArray1 = java.lang.Strin

60、gone; strArray2 = java.lang.Stringtwo; strArray3 = java.lang.Stringthree; cellArray = cellstrArray This code returns cellArray = one two three Create a cell array of folders in the c:work folder, using the .NET Framework System.IO.Directory class : myList = cellSystem.IO.Directory.GetDirectoriesc:wo