MATLAB Basics

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MATLAB Basics
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• Workspace
• variable list
• includes size and type

Command window
Command history
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• instructions or commands are typed directly into
  the Command Window
• every command generates a result which is shown
  in the Command Window after the instruction
• a value of 3 has been assigned to variable a
• numeric variables are stored in arrays
• Workspace Window indicates that the variable a is
  a 1x1 matrix holding a double precision value
  which requires 8 bytes of storage.
• note that the assignment command was recorded in
  the Command History Window

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• each command is executed as it is entered
• value of 4 is assigned to variable b
• sum of the values assigned to a and b is assigned
  to variable c and result is immediately displayed
• if the result of a command is not assigned to a
  named variable, then the result is assigned to
  the default variable ans
• workspace now contains 4 variables
• line spacing in the Command Window can be reduced
  by setting the format to compact
• the Command Window will scroll automatically or
  it can be completely cleared by issuing the clc
  command

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• the workspace can be emptied by issuing the clear
  command

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• these commands produce the calculated volume of a
  cylindrical tank, d 3 ft, h 4 ft
• note that the value for pi is predefined
• the resolution of calculated results can be
  changed by using the commands format long and
  format short
• note that variable names are case sensitive,
  i.e., a and A are two different variables that
  stored separately in the workspace

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• arrays or matrices are entered row by row with
  the column separated by spaces and the rows
  separated by semicolons.
• rows may be split between multiple command lines
• standard linear algebra operations are applied
  directly to the matrix variables
• individual array elements are selected by placing
  the row and column indices in parentheses
• the selected element may be displayed or changed

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• the colon operator is used to generate
  sequences of numbers
• syntax is firstincrementlast
• increment may be positive or negative so the
  sequence can be increasing or decreasing

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• transpose of a matrix is generated by placing an
  apostrophe after the matrix name or expression
• transpose of a row vector is a column vector

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• Linear equation set in matrix format
• simple method for solving simultaneous linear
  equation set is to use the left-divide or
  backslash operator
• c a\b is functionally equivalent to c
  inverse(a)b
• actual method used for the solution is based on
  Gauss elimination rather a matrix inverse

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• plots are generated from arrays of the coordinate
  data
• the plot appears in a separate Plot Window

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• plot of cos(x) for 11 equally spaced values of x
  between -pi and pi
• math functions are applied to matrices on an
  element by element basis
• resulting plot needs more data points to generate
  a smooth curve

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• generate 201 equally spaced value of x between
  pi and pi
• to avoid generating a listing of the coordinate
  data, suppress the output from an individual
  command by placing a semicolon at the end

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• rather than repeatedly typing commands, it would
  be easier to define a script for a sequence of
  commands.
• matlab stores command scripts in m-files
• first, pick a storage location for your files
• click on the Current Directory tab
• click on the small white rectangle near the path
  name to browse the directory structure
• create a directory to hold all matlab work

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• select File/New/M-file
• a separate Matlab edit window is opened for the
  creation of the matlab script
• enter the commands necessary to calculate the
  cylindrical tank volume
• save the file as volume.m

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Tank Filling Time Equations
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• Create the program with separate sections for the
  Constants and Calculations
• Note that the lines are ended with a semicolon
  () which suppresses the execution output for
  that line
• A program line must be terminated with a
  semicolon before tabbing over for the comment
• The percent () character marks the beginning of
  a comment
• Read the description of the disp function in
  the matlab help
• Save the m-file in the Current Directory as
  tank.m

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• Execute the program by typing the file name in
  the command window.

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• Add an Input section to the program to allow the
  user to specify the velocity at each inlet
• Delete the inlet velocity initializations that
  were in the Constants section
• Read about the input function in the matlab
  help facility
• Save the changes

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• Clear the Workspace
• Run the program
• Use the same inlet velocities to check that the
  same result is obtained