CPET 190

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CPET 190

• Problem Solving with MATLAB
• Lecture 14
• Professor Paul Lin
• http//www.etcs.ipfw.edu/lin

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MATLAB Standard I/Os

• Standard I/Os
• Standard input - keyboard
• Standard output monitor screen
• Standard error device monitor screen
• MATLAB I/Os
• keyboard input
• Filename input(Enter a file name , s)
• Monitor output
• disp( ) function display an array or text
  string
• fprintf( format,data) function display data
  with desired format

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Lecture 14 File Input and Output

• MATLAB I/O Functions
• diary( ) save text of MATLAB session
• gtgt diary
• save( ) save workspace variable to disk
• gtgt save FILENAME
• load( ) load workspace variables from disk
• gtgt load FILENAME
• textread( ) read formatted data from text file

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Save and Load Function

• save function
• load function

gtgt save 8_20_2004.mat gtgt clear gtgt whos gtgt load
8_20_2004.mat gtgt whos Name Size Bytes
Class ans 1x1 8 double array
x 1x1 8 double array y
1x1 8 double array Grand total
is 3 elements using 24 bytes gtgt clear gtgt whos
Current Directory
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MATLAB File Formats

• gtgthelp filefomats
• Data formats Commands Returns
• MAT - MATLAB workspace load Variables in
  file.
• CSV - Comma separated numbers csvread
  Double array.
• DAT - Formatted text importdata Double array.
• DLM - Delimited text dlmread Double array.
• TAB - Tab separated text dlmread Double array.
• Spreadsheet formats
• XLS - Excel worksheet xlsread Double array and
  cell array.
• WK1 - Lotus 123 worksheet wk1read Double array
  and cell array.
• Scientific data formats
• CDF - Common Data Format cdfread Cell array of
  CDF records
• FITS - Flexible Image Transport System
  fitsread Primary or extension table data
• HDF - Hierarchical Data Format hdfread HDF or
  HDF-EOS data set
• Movie formats
• AVI - Movie aviread MATLAB movie.

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MATLAB File Formats

• gtgthelp filefomats
• Data formats Command Returns
• Image formats
• TIFF - TIFF image imread Truecolor, grayscale or
  indexed image(s).
• PNG - PNG image imread Truecolor, grayscale or
  indexed image.
• HDF - HDF image imread Truecolor or indexed
  image(s).
• BMP - BMP image imread Truecolor or indexed
  image.
• JPEG - JPEG image imread Truecolor or grayscale
  image.
• GIF - GIF image imread Indexed image.
• PCX - PCX image imread Indexed image.
• XWD - XWD image imread Indexed image.
• CUR - Cursor image imread Indexed image.
• ICO - Icon image imread Indexed image.
• RAS - Sun raster image imread Truecolor or
  indexed.
• PBM - PBM image imread Grayscale image.
• PGM - PGM image imread Grayscale image.
• PPM - PPM image imread Truecolor image.
• Audio formats

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MATLAB Low-Level File I/Os

• File Opening and Closing Functions
• fopen( ) open file for reading, writing, or
  appending
• fclose( ) close file or files
• Binary I/O
• fread( ) read binary data from file
• fwirte( ) write binary data to file
• Formatted I/O
• fscanf( ) read formatted data from file
• fprintf( ) write formatted data to file
• fgets( ) read line from file, keep newline
  character
• fgetl( ) read line form file, discard newline
  character

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MATLAB Low-Level File I/Os (continued)

• String Conversion Functions
• sprinf( ) write formatted data to string
• sscanf( ) read string under format control
• File Positioning Functions
• ferros( ) File I/O error status
• feof( ) test for end of file
• fseek( ) set file position indicator
• ftell( ) get file position indicator
• frewind( ) Rewind file

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File Path

• Set File Path
• File -gt Set Path -gt Add Folder
• MTALAB Path Search -gt G\public_html\cpet190\codes
  
• Click on Save button, and then Close button

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Example 14-1 Loading a Sequence of Data Files

• Create dataFiles
• gtgt x -100.110
• gtgt y 2(x.2) 1
• gtgt save dataFile1
• gtgt clear y
• gtgt y 2(x.2) 10
• gtgt save dataFile2
• To open a sequence of enumerated data files
• for file_no 1 N
• fname sprintf(testDatad,file_no)
• load(fname)
• end

• Create dataFiles
• gtgt whos
• Name Size Bytes Class
• N 1x1 8 double array
• file_no 1x1 8 double array
• Fname 1x9 18 char array
• x 1x201 1608 double array
• y 1x201 1608 double array
• z 1x201 1608 double array
• gtgt plot(x , y)
• gtgt plot(x, z)

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File Processing

• Reading a file
• Open a file for reading
• Process reading from the file
• Close the file
• Appending to a file
• Open a file for appending
• Process appending the file
• Close the file
• Writing to a file
• Open a file for writing
• Process writing to the file
• Close the file

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Typical File Processing

• Open files
• fid fopen(' file_name ', permissions), where
  permissions can be one of the following
• 'r - Open the file for reading. The file must
  exist. An error occurs if the file does not
  exist.
• 'r - Open the file for reading and writing. The
  file mut exist. An error occure if the file does
  not exist
• 'w - Open the file for writing, create if
  necessary
• 'w - Truncate or create for read and write
• 'a - Append (create if necessary)
• 'a Read and append (create if necessary)
• Write to, Read from files
• Close files

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Example 14-2 Create a file - a table of the
exponential function

• Pseudo Code
• 1. Create x and y vectors for exponential
  function
• 2. Open A File for Writing
• 3. Write Formatted Data fprinf(fid, format
  specifiers, data)
• 4. Close File
• The program
• save_exp.m
• x 0.11 y x' exp(x)'
• fid fopen('expfucntion.txt','w')
• fprintf(fid,'f f\n', y)
• fclose(fid)

File Content 0 1.0000 0.1000
1.1052 0.2000 1.2214 0.3000 1.3499
0.4000 1.4918 0.5000 1.6487
0.6000 1.8221 0.7000 2.0138 0.8000
2.2255 0.9000 2.4596 1.0000 2.7183
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Example 14-2 Create a file - a table of the
exponential function

• We edit the program as shown in previous slide
• Set default directory or folder for storing the
  file
• Debug or test the program through the MATLAB
  M-file editor
• Open Windows Explorer and examine the created
  file

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Example 14-2 Create a file - a table of the
exponential function

• Open the expfunction.txt file using Microsoft
  Wordpad
• Open the expfunction.txt file using Notepad

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Example 14-3 Reading Exponential Function File
for Plotting

• load_exp.m
• fid fopen('expfucntion.txt','r')
• Retrieve data table a 11-by-2
• y1 count fscanf(fid,'f', 11 2)
• fclose(fid)
• Extract first column
• x y1(,1)
• Extract 2nd column
• exp_x y1(,2)
• plot(x, exp_x) grid on

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Example 14-4 Writing and Reading Binary Data

• binary_file.m
• filename input('Enter a file name ', 's')
• out_data 100rand(10, 1)
• fid msg fopen(filename,'w')
• File open OK?
• if fid gt 0
• count fwrite(fid, out_data, 'double')
• disp(int2str(count) ' value written to disk
  ..')
• status fclose(fid)
• else
• Failed to open the file
• disp(msg)
• end

Open the file for reading fid msg
fopen(filename, 'r') if fid gt 0 in_data,
count fread(fid, 10, 'double')
disp(int2str(count) ' value read from the disk
..') status fclose(fid) else
Failed to open the file disp(msg) end in_data
out_data
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Example 14-4 Writing and Reading Binary Data

• binary_file.m
• filename input('Enter a file name ', 's')
• out_data 100rand(10, 1)
• fid msg fopen(filename,'w')
• File open OK?
• if fid gt 0
• count fwrite(fid, out_data, 'double')
• disp(int2str(count) ' value written to disk
  ..')
• status fclose(fid)
• else
• Failed to open the file
• disp(msg)
• end

Open the file for reading fid msg
fopen(filename, 'r') if fid gt 0 in_data,
count fread(fid, 10, 'double')
disp(int2str(count) ' value read from the disk
..') status fclose(fid) else
Failed to open the file disp(msg) end in_data
out_data
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Example 14-4 Writing and Reading Binary Data

• in_data
• 95.0129
• 23.1139
• 60.6843
• 48.5982
• 89.1299
• 76.2097
• 45.6468
• 1.8504
• 82.1407
• 44.4703

out_data 95.0129 23.1139 60.6843
48.5982 89.1299 76.2097 45.6468
1.8504 82.1407 44.4703
Binary Files - Not Readable
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Summary

• MATLAB Standard I/Os - File Input and Output
• Save and Load Function
• MATLAB File Formats
• MATLAB Low-Level File I/Os
• File Path
• File Processing Examples
• Formatted Files
• Binary Files
• Be sure to read Chapter 8 of the Text book,
  MATLAB help