MATLAB Input-Output Statements - PowerPoint Presentation

1. MATLAB Input-Output Statements

2. IntroductionData Input: Three methods1. Assign data to variables through an assignment statement 2. Input data from Keyboard 3. Read data from a file stored in computer memory

3. Data Input 1. Assign data to variables through an assignment statement >>x=2;>>y=34.2;>>name=“Raheel Sufyaan”; or >>x=2; y=34.2; name=“Raheel Sufyaan”;

4. Data Input 2. Input data from Keyboard (Interactive input)Input Function Keyboard Command menu function pause command

5. Data Input I. Input Function : See different version of this function >>r=input(‘Enter radius in meters:’)Enter radius in meters:56 %r will become integer r = 56Enter radius in meters: ’ninety six’ %r will become string , Note: ‘ ‘ compulsory r = ninety six >>r=input(‘what is your father’s name:’, ’s’) %s for string, what is your father’s name: Nafees Ahmed % Note: ‘ ‘ not requiredr = Nafees Ahmed

6. Data Input II. ‘Keyboard’ & ‘return’ command ‘keyboard’ command when included in a script file returns control to the keyboard at the point where command occurs. The command window prompt is prefixed by the letter ‘k’. This command is used for Check the intermediate results in the program Make changes in variables value if required Add new MATLAB commands in the programExp: Make a .m file for the following code and run it A=10;B=16;X=A+B;Y=X/2;Keyboard %check the value of Y and change Y=10, after finishing write %‘return’ command, it will execute rest program Z=A-B

7. Data Input III. ‘menu’ function for pictorial selection. Syntax is I=menu(‘title’, ‘option1’, ‘option2’,……..)Exp: Make a .m file for the following code and run it i=menu('Select your favorite name','Teenu','Sumbul','Humera');if i==1 disp('Teenu is your wife')elseif i==2 disp('Sumbul is yr sis-in-low')elseif i==3 disp('Humera is yr sis-in-low')else disp('Bewakoof kuch to select karo')end

8. Data Input IV. ‘pause’ command ‘pause’ command temporarily halts the current computation and waits for the user to give a command to resume the computations. Pressing any key resumes the computation. pause(k) command stops the computation for k seconds. Exp: Make a .m file for the following code and run it P=[1 2; 3 4]; Q=[5 5; 7 8];disp('The matrix P is given as:')disp(P)disp('Program is paused, please press any key to display matrix Q')pausedisp('The matrix Q is given as:')disp(Q)Z=P+Q;disp('Program is paused, please press any key to display sum of P & Q')pausedisp(Z)disp('Again program is pausing for 5 sec')pause(5)

9. Reading and storing file data There are many functions which are used to get data from the files.1.’load’ function: To load variables/data in workspace from the disk fileDifferent syntax are load %load matlab.mat (default) file Load(‘filename’) %load complete file whose name is given Load(‘filename’, ’x’, ’y’, ’z’) %load only variables x, y, z of given file Load filename x, y, z %same as above Note:- No extension with file name means .mat file If file name has extension other than (.mat) it will be treated as ASCII data fileLoad function is use only if data file contains numeric data

10. Reading and storing file data Exp: >>edit abc.txtWrite following and save it 3 4 5 77 8 0 9 >>load abc.txt %it will load this file in workspace with a variable %name abc, to check it write abc >>abc3 4 5 77 8 0 9 If we want to change the variable name write following command >>test=load (‘abc.txt’) %now data ‘abc.txt’ will store in variable ‘test’

11. Reading and storing file data 2.’save’ function: To save current workspace data/variables to disk fileDifferent syntax are save %save all workspace data in matlab.mat file save(‘filename’) %save complete workspace data in specified file name save(‘filename’, ’x’, ’y’, ’z’) %save only variables x, y, z in a file save filename x, y, z %same as above Note:- No extension with file name means .mat file If file name has extension other than (.mat) it will be treated as ASCII data fileTo save variables to a directory other than current directory, full pathname of the file has to be specified.

12. Reading and storing file data 3.’dlmread’ function: To read numeric text data separated by character other than space.(dlm=>delimiter, by default delimiter is comma )Different syntax are data=dlmread(‘filename’) %read numeric data from ASCII delimited file named filename data=dlmread(‘filename’, delimiter) %read numeric data from ASCII delimited with other delimiter i.e.var_name=dlmread(‘abc.txt’, ‘;’) % this will read the data from file abc.txt till it encounters ‘;’ delimiter. For example see next slide

13. Reading and storing file data 4.’dlmwrite’ function: To write numeric text data separated by character other than space. (dlm=>delimiter, by default delimiter is comma )Different syntax are dlmwrite(‘filename’,A) %write matrix ‘A’ on a specified file name with default delimiter (,)dlmwrite(‘filename’, A, ‘D’) % write matrix ‘A’ on a specified file name with default delimiter ‘D’ i.e.>>A=[1 2 3; 4 5 6; 7 8 9]>>dlmwrite(‘abcd.txt’, A,‘D’) % this will write matrix A on file abcd.txt with delimiter ‘D’. Open this file & See. Now try>>B=dlmread(‘abcd.txt’,’D’)

14. Reading and storing file data 5.’textscan’ and ‘textread’ functions: If a text file contains numeric as well as other characters. The file need to be opened for read operation using ‘fopen’ command & then read using ‘textscan’ command.Different syntax are fid=fopen(‘abc.txt’, ’r’) %Open abc.dat file for reading var_name=textscan(fid, ‘%f %c …….’) %here %f for float, %c for char etc Note: var_name will be cell array The command textread can be used to read the data into separate variables. [a, b, c, d]=textread(‘abc.txt”, ‘%f %c …….’) i.e.[name, types, a, b, c]=textread(‘abc.txt’, ’%s %s %f %f %f’)

15. Output commands1. Output may be formatted or unformatted Default format : >>a=7a= 7>>b=1.01b= 1.0100 %4 digit after decimal >>2100.34c= 2.1003e+003 %2.1003x103Format command to change default format>>x=pix = 3.1416>>format long %similarly we can have other format also see help x = 3.141592653589793

16. Output commands‘disp’ function >>A=[1 2; 3 4]; % to display variable >>disp(A) 1 2 3 4>>disp(‘The largest number is;’) %to display a message The largest number is

17. Low-level input-output functions There are a number of low-level file input-output function in MATLAB taken from ANSI Standard C Library. These are 1. File opening and closing functions2. Binary input-output functions 3. Formatted input-output functions

18. Low-level input-output functions 1. File opening and closing functions‘fopen’ function: To perform any operation on file the first step is open it. Syntax are fid=fopen( filename, permission_code) where fid=file id permission_code = read or write or append [fid, message] = fopen(filename, permission_code) where message = error msg if file doesn’t open properly otherwise it is empty string [fid, message] = fopen(filename, permission_code, format) where format = optional string specifying the numeric format of the data in the file

19. Low-level input-output functions Standard file identifier values Note: As more files are opened fids are allotted in continuation and if a particular file is closed, the fid assigned to it is released.fid Meaning -1Fid opening fails0Standard input (keyboard)1Standard output (monitor screen)2Standard error 3 onwards Assign to file opened successfully

20. Low-level input-output functions Permission code Note: As more files are opened fids are allotted in continuation and if a particular file is closed, the fid assigned to it is released.Permission text string Meaning rOpen a file(default) for reading, if not exist error occurs r+Open a file(default) for reading & writing, if not exist error occurs wDelete the contents of an existing file or create a new file, and open it for writing.w+Delete the contents of an existing file or create new file, and open it for reading and writing.aCreate and open a new file or open an existing file for writing, appending to the end of the file.a+Create and open new file or open an existing file for reading and writing, appending to the end of the file.

21. Low-level input-output functions Other use of ‘fopen’ function: fids=fopen(‘all’) where fids=a vector showing file ids of all opened files [filename, permission_code, format] = fopen(fid) This function provieds filename, permission_code & format for open file specified by fid

22. Low-level input-output functions ‘fclose’ function: After performing operations on file the last step is to close it. Syntax are status = fclose( fid) where status= 0 if successfully closed =-1 otherwise status = fclose(‘all’) It closes all open files except for standard output(fid = 1) & standard error (fid = 2) Note: Standard input, output & error can’t be opened or closed with fopen & fclose functions

23. Low-level input-output functions Formatted input-output functions: These are used to print, scan or get data in desired format. Different functions arefprintf function fscanf functionfgetl functionfgets function

24. Low-level input-output functions ‘fprintf ‘ function: Syntax is fprintf(fid, format, data)Exp: Create a file having following code and rut it.x = 0:.1:1; y = [x; exp(x)];fid = fopen('exp.txt','w');fprintf(fid,'%6.2f %12.8f\n', y);fclose(fid);Now open the file ‘exp.txt’ and see the data Note: 1. Here %6.2f . it always starts with % sign 6 = total width of field 2 = no of digits after decimal f = fixed point 2. fprintf(‘%6.2f %12.8f\n’, y ) will print on monitor, here fid =0 i.e monitor

25. Low-level input-output functions In general ‘format’ may be written as %a.beOr %+a.be % + = always print with sign character (+ or -)Or %-a.be % - = left justified Or %0a.be % pad zeros in starting Here a = field width b = digits after decimal point e = conversion character (%c for char, %s for string, %d for int, %e for exponential, %f for fixed point etc) Note: 1. '%6.2f %12.8f\n‘ here note the space b/w to formats 2. \n means new line 3. ‘fprintf ‘ displays only real portion of complex value

26. Low-level input-output functions ‘fscanf ‘ function: Syntax is fscanf(fid, format)And [A, count] = fscanf(fid, format, sizeA)Where A = variable to store data count = no of values reads from the files sizeA = size of matrix A Exp: Read the data of previously created file ‘exp.txt’. Create a file having following code and rut it.fid = fopen('exp.txt');A = fscanf(fid, '%g %g', [2 inf]); % A is 2 row x inf column matrix A=A’ % transpose to get the original matrix fclose(fid);

27. Low-level input-output functions ‘fgetl ‘ function: Reads the next line of the specified file, removing the newline characters. Syntax is statement=fgetl(fid) Exp: Read and display the file fgetl.m one line at a time: fid = fopen('fgetl.m'); tline = fgetl(fid); while ischar(tline) disp(tline) tline = fgetl(fid); end fclose(fid);

28. Low-level input-output functions ‘fgets ‘ function: Reads the next line of the specified file, including the newline characters Syntax is statement=fgets(fid) Exp: Read and display the file fgetl.m one line at a time: fid = fopen('fgetl.m'); tline = fgets(fid); while ischar(tline) disp(tline) tline = fgets(fid); end fclose(fid);

29. Low-level input-output functions Binary input-output functions: The formatted input-output functions works with human readable text in a file. This file is also called an ASCII text file. These files require more disk space as compared to binary files. Different functions for binary files system are‘fwrite’ function ‘fread’ function

30. Low-level input-output functions ‘fwrite’ function: Syntax is count=fwrite(fid, array, ‘percision’)Where count = no of values (data) written to file fid = file id array = array of values to be written precision = format of storing the values (char, uchar, short, int, long, float, double)

31. Low-level input-output functions Exp: Please make a .m file of following code and run it. a=[2 3 6; 3 5 7];b=105;c='IPL has started';fid=fopen('check.txt','w');x=fwrite(fid,a, 'double') %a is ‘double’ y=fwrite(fid, b, 'int') %b is an int constant z=fwrite(fid,c, 'char') %c is a char string fclose(fid);

32. Low-level input-output functions ‘fread’ function: Syntax is [variable, count]=fread(fid, size, ‘percision’)Where variable= values to be read from file size = dimensions of data to be readNote: To read binary data from a file correctly, it must be know how it was written

33. Low-level input-output functions Exp: Please make a .m file of following code and run it. fid=fopen('check.txt','r');[A, count1]=fread(fid, [2,3], 'double') %A is ‘double’ 2x3 matrix [B, count2]=fread(fid, [1], 'int') %B is an int constant [C, count3]=fread(fid, [inf], 'char') %C is a char string C=setstr(C) %convert data into string C=C'; %transpose Cfclose(fid);

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