Introduction to MATLAB

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Introduction to MATLAB
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Outline

• Introduction
• MATLAB Environment
• Getting Help
• Vectors, Matrices, and Linear Algebra
• Plotting
• User Defined Functions
• Image Manipulation and Processing
• Audio Processing
• Filters and Operations

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Introduction

• MATLAB Stands for MATrix LABoratory.
• The MATLAB environment allows the user to
• manage variables
• import and export data
• perform calculations
• generate plots
• develop and manage files for use with MATLAB.
• A script can be made with a list of MATLAB
  commands like other programming language.

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Environment
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Getting Help

• Type one of following commands in the command
  window
• help lists all the help topic
• help topic provides help for the specified
  topic
• help command provides help for the specified
  command
• help help provides information on use of the
  help command
• helpwin opens a separate help window for
  navigation
• lookfor keyword Search all M-files for keyword
• Or simply press F1 and use the graphical help
  window.

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Variables

• Variable names
• Must start with a letter
• May contain only letters, digits, and the
  underscore _
• Matlab is case sensitive, i.e. one OnE are
  different variables.
• Matlab only recognizes the first 31 characters in
  a variable name.
• when a semi-colon
• gtgt tutorial 1234
• gtgt tutorial 1234
• is placed at the end of each command, the
  result is not displayed.

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Variables (Contd)

• Special variables
• ans default variable name for the result
• pi p 3.1415926
• eps ? 2.2204e-016, smallest amount by which 2
  numbers can differ.
• Inf or inf 8, infinity
• NaN or nan not-a-number
• Commands involving variables
• who lists the names of defined variables
• whos lists the names and sizes of defined
  variables
• clear clears all variables, reset the default
  values of special variables.
• clear name clears the variable name
• clc clears the command window
• clf clears the current figure and the graph
  window.

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Vectors

• gtgt x 0 0.25pi 0.5pi 0.75pi pi
• x
• 0 0.7854 1.5708 2.3562 3.1416
• gtgt y 0 0 25pi 0 5pi 0 75pi
• y
• 0
• 0.7854
• 1.5708 y
• 2.3562
• 3.1416

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Vectors (Contd)

• Vector Addressing A vector element is addressed
  in MATLAB with an integer index enclosed in
  parentheses.
• gtgt x(3)
• The colon notation may be used to address a block
  of elements (start increment end)
• start is the starting index, increment is the
  amount to add to each successive index, and end
  is the ending index. A shortened format (start
  end) may be used if increment is 1.
• gtgt x(13)
• ans
• 0 0.7854 1.5708
• NOTE MATLAB index starts at 1.

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Vectors (Contd)
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Array Operations

• Scalar-Array Mathematics
• Element-by-Element Array-ArrayMathematics

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Matrices

• A Matrix array is two-dimensional, having both
  multiple rows and multiple columns, similar to
  vector arrays
• It begins with , and end with
• spaces or commas are used to separate elements in
  a row
• semicolon or enter is used to separate rows.
• Matrix Addressing
• matrixname(row, column)
• colon may be used in place of a row or column
  reference to select the entire row or column.

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Matrices (Contd)
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Matrices (Contd)
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Example, Linear Equations
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Plotting

• Plotting Curves
• plot (x,y) generates a linear plot of the
  values of x (horizontal axis) and y (vertical
  axis).
• semilogx (x,y) generate a plot of the values of
  x and y using a logarithmic scale for x and a
  linear scale for y
• semilogy (x,y) generate a plot of the values of
  x and y using a linear scale for x and a
  logarithmic scale for y.
• loglog(x,y) generate a plot of the values of x
  and y using logarithmic scales for both x and y
• Multiple Curves
• plot (x, y, w, z) multiple curves can be
  plotted on the same graph by using multiple
  arguments in a plot command. The variables x, y,
  w, and z are vectors. Two curves will be plotted
  y vs. x, and z vs. w.
• legend (string1, string2,) used to
  distinguish between plots on the same graph
• Multiple Figures
• figure (n) used in creation of multiple plot
  windows. place this command before the plot()
  command, and the corresponding figure will be
  labeled as Figure n
• close closes the figure n window.
• close all closes all the figure windows.
• Subplots
• subplot (m, n, p) m by n grid of windows, with
  p specifying the current plot as the pth window

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Plotting (Contd)
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Flow Control
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Loops

• break is used to terminate the execution of the
  loop.

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M-Files

• A M-file is a group of MATLAB commands.
• MATLAB can open and execute the commands exactly
  as if they were entered at the MATLAB command
  window.
• To run the M-files, just type the file name in
  the command window. (make sure the current
  working directory is set correctly)

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User Defined Functions

• Add the following command in the beginning of
  your m-file
• function output variables function_name
  (input variables)
• Note that the file name should be the same as the
  function name.

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Images in MATLAB

• MATLAB can import/export several image formats
• BMP (Microsoft Windows Bitmap)
• GIF (Graphics Interchange Files)
• HDF (Hierarchical Data Format)
• JPEG (Joint Photographic Experts Group)
• PCX (Paintbrush)
• PNG (Portable Network Graphics)
• TIFF (Tagged Image File Format)
• XWD (X Window Dump)
• MATLAB can also load raw-data or other types of
  image data

• Data types in MATLAB
• Double (64-bit double-precision floating point)
• Single (32-bit single-precision floating point)
• Int32 (32-bit signed integer)
• Int16 (16-bit signed integer)
• Int8 (8-bit signed integer)
• Uint32 (32-bit unsigned integer)
• Uint16 (16-bit unsigned integer)
• Uint8 (8-bit unsigned integer)

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Images in MATLAB

• Binary images 0,1
• Intensity images 0,1 or uint8, double etc.
• RGB images m-by-n-by-3
• Indexed images m-by-3 color map
• Multidimensional images m-by-n-by-p (p is the
  number of layers)

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Image import and export

• Read and write images in Matlab
• gtgt Iimread('cells.jpg')
• gtgt imshow(I)
• gtgt size(I)
• ans 479 600 3 (RGB image)
• gtgt Igreyrgb2gray(I)
• gtgt imshow(Igrey)
• gtgt imwrite(lgrey, 'cell_gray.tif', 'tiff')
• Alternatives to imshow
• gtgtimagesc(I)
• gtgtimtool(I)
• gtgtimage(I)

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Images and Matrices

• How to build a matrix (or image)?
• gtgt A 1 2 3 4 5 6 7 8 9
• A 1 2 3
• 4 5 6
• 7 8 9
• gtgt B zeros(3,3)
• B 0 0 0
• 0 0 0
• 0 0 0
• gtgt C ones(3,3)
• C 1 1 1
• 1 1 1
• 1 1 1
• gtgtimshow(A) (imshow(A,) to get automatic
  pixel range)

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Image format conversion

• Convert between intensity/indexed/RGB to binary
  format
• dither()
• Convert between intensity format to indexed
  format
• gray2ind()
• Convert between indexed format to intensity
  format
• ind2gray()
• Convert between indexed format to RGB format
• ind2rgb()
• Convert a regular matrix to intensity format by
  scaling
• mat2gray()
• Convert between RGB format to intensity format
• rgb2gray()
• Convert between RGB format to indexed format
• rgb2ind()

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Colormaps

• I imread (lena.bmp)
• imshow (I)
• colormap (cool)
• Autumn, bone, colorcube, cool, copper, flag,
  gray, hot, hsv, jet, pink, prism, spring, summer,
  white, winter

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Video

• mov aviread(filename)
• mov aviread(filename, index)
• fileinfo aviinfo(filename)

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Digital Audio
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Audio

• road,fswavread('road.wav')
• The array road now contains the stereo sound data
  and fs is the sampling frequency. 
• This data is sampled at the same rate as that on
  a music CD (fs44,100 samples/second).
• The left and right channel signals are the two
  columns of the road array
•  leftroad(,1)
• rightroad(,2)

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• time(1/44100)length(left)
• tlinspace(0,time,length(left))
• plot(t,left)
• xlabel('time (sec)')
• ylabel('relative signal strength')
• soundsc(left,fs)       plays left channel as
  mono
•  soundsc(right,fs)    plays right channel mono
  (sound nearly the same)
•  soundsc(road,fs)     plays stereo (ahhh)

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