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MATLAB Input-Output Statements

MATLAB Input-Output Statements. Nafees Ahmed Asstt. Professor, EE Deptt DIT, DehraDun. Introduction. Data Input: Three methods 1. Assign data to variables through an assignment statement 2. Input data from Keyboard 3. Read data from a file stored in computer memory. Data Input .

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MATLAB Input-Output Statements

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  1. MATLAB Input-Output Statements Nafees Ahmed Asstt. Professor, EE Deptt DIT, DehraDun

  2. Introduction • Data Input: • Three methods • 1. 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 = 56 Enter radius in meters: ’ninety six’ %r will become string , Note: ‘ ‘ compulsory r = ninety six >>r=input(‘what is your father’s name:’, ’s’) %r string, what is your father’s name: Nafees Ahmed % Note: ‘ ‘ not required r = 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 program Exp: 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') elseifi==2 disp('Sumbul is yr sis-in-low') elseifi==3 disp('Humera is yr sis-in-low') else disp('Bewakoofkuch 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') pause disp('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') pause disp(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 file Different 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 file • Load function is use only if data file contains numeric data

  10. Reading and storing file data Exp: >>edit abc.txt Write following and save it • 3 4 5 7 • 7 8 0 9 >>load abc.txt %it will load this file in workspace with a variable %name abc, to check it write abc >>abc • 3 4 5 7 • 7 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 variables/data from workspace to disk file Different 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 file • To 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 commands 1. Output may be formatted or unformatted • Default format : >>a=7 a= 7 >>b=1.01 b= 1.0100 %4 digit after decimal >>2100.34 c= 2.1003e+003 %2.1003x103 • Format command to change default format >>x=pi x = 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 functions 2. 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.

  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.

  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 are • fprintf function • fscanf function • fgetl function • fgets 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.be Or %+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. clear all %clear all variable in workspace 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=C' %transpose of C C=char(C) %Convert numeric values into character 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 read • Note: 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. a=[2 3 6; 3 5 7]; b=105; c='IPL has started'; 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 fclose(fid)

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