Distance Learning Center

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Distance Learning Center

• Lecture 7
• Problem Solving with MATLAB
• Melissa Lin, IT Consultant
• HenEm, Inc. Parkville, Missouri
• linm_at_ipfw.edu
• http//www.etcs.ipfw.edu/linm

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Lecture 7 MATLAB Built-In Functions

• 7-1 Managing Variables and Workspace
• 7-2 MATLAB Commands for Working with Files and
  the Operating System
• 7-3 Controlling Command Window
• 7-4 Time and Date Functions
• 7-5 Special Variables and Constants

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7-1 Managing Variables and Workspace

• Removing Unneeded Variables
• who - List current variables
• whos - List current variables, long form
• clear - Clear variables and functions
• Creating New Variables
• length - Length of vector
• size - Size of matrix
• Saving to and Retrieving from Disk Files
• load - Retrieve variables from disks
• save - Save workspace variables to disk
• pack - Consolidate workspace memory
• Workspace display
• disp - Display matrix or text
• fprintf

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7-1 Managing Variables and Workspace (continue)

• Example 7-1
• cpet190_ex7_1.m
• F 4000
• T 1/F
• dt 0.01T
• t 0dt2T
• e1 5sin(2piFt)
• len length(e1)
• size_e1 size(e1)
• e2 zeros(size(e1))
• num rand(2)

fprintf('The random number array is g\n',
num) fprintf('\n') disp('The random
numbers') disp(num) whos save ex7_1 clear load
ex7_1 whos
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7-1 Managing Variables and Workspace

• Example 7-1 Output

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7-2 Working with Files and OS

• The commands for working with files and operating
  system
• Command Purpose
• pwd Show present working directory
• cd Change current working directory
• dir Directory listing (Window OS)
• ls Directory Listing (Unix/Linux OS)
• delete Delete file
• diary Save text of MATLAB session
• ! Execute OS commands

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7-2 Working with Files and OS

• Example 7-2 (cont.)
• gtgt diary
• gtgt diary off
• gtgt diary on
• gtgt !time
• The current time is 113105.02
• Enter the new time
• Open diary file using MATLAB M-file editor, MS
  NOTEPAD, or MS Word
• help

• Example 7-2
• gtgt pwd
• ans
• C\Courses\CPET190\matlabex190
• gtgt cd ..
• gtgt pwd
• ans
• C\Courses\CPET190
• gtgt dir
• . Mlin_CPET190
• .. Exs
• Quiz Lectures
• MATLABExs

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7-3 Controlling the Command Window

• clc Clear command window
• home Send cursor home (upper-left corner
• of command window)
• format Set output format
• more Control paged output in command
• window
• echo Echo on/off commands inside script
• files, for debugging purposes

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7-4 Time and Date Functions

• Function Purpose
• date Calendar
• clock System clock accuracy 1/100th of a second
• now Current date and time as serial date number
• datestr Convert a serial date number into the
  common date/time, save as a string
• cputime How many seconds the MATLAB session is
  active accuracy 1/100 th of second
• etime Elapsed time function
• tic Start watch timer function
• toc Stop watch timer function

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7-4 Time and Date Functions

• Time and Date Functions
• Example 7-3
• gtgt date
• ans
• 03-Oct-2004
• gtgt now
• ans
• 7.3222e005
• gtgt datestr(now)
• ans
• 03-Oct-2004 124729
• gtgt help datestr

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7-4 Time and Date Functions (continue)

• CLOCK Current date and time as date vector.
• CLOCK returns a six element date vector
  containing the
• current time and date in decimal form
• CLOCK year month day hour minute
  seconds
• The first five elements are integers. The
  seconds element
• is accurate to several digits beyond the
  decimal point.
• FIX(CLOCK) rounds to integer display format.
• Example
• gtgt clock
• ans
• 1.0e003
• 2.0040 0.0100 0.0030 0.0120
  0.0410 0.0071

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7-4 Time and Date Functions (continue)

• Example 7-4 measuring program execution time
  (accuracy 1/100 th of a second) using cputime
  function

t1_1 cputime for i 11000 num_array
inv(rand(30)) end t1_2 cputime time_1000
t1_2 - t1_1 time_once time_1000/1000
time_1000 0.3610 time_once 3.6100e-004
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7-4 Time and Date Functions

• Example 7-5 measuring program execution time
  (accuracy 1/100 th of a second) using tic and
  toc functions

tic for i 11000 num_array
inv(rand(30)) end toc
elapsed_time 0.3610
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7-5 Special Variables and Constants

• Example 7-6 AC circuit calculation using complex
  numbers.
• A RLC circuit is shown on this slide, find
• Total impedance Z
• Voltage and current across each components

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7-5 Special Variables and Constants (continue)

• Example 7-6
• Analysis Domain knowledge
• XL 2pfL, where L is the inductance in Henry, f
  is the frequency of ac source
• XC 1/(2 pfC), where C is the capacitance in
  Farard
• Z R j(XL XC) -- total impedance, where j
  shows the imaginary component of a complex number
  
• I E/Z, total current
• VR IR, voltage drop across resistor
• VL IXL, voltage drop across the inductor
• VC IXC voltage drop across the capacitor

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7-5 Special Variables and Constants (continue)

• Example 7-6 MATLAB Program
• RLC_1.m
• f 60 R 8
• Peak value of the sine wave
• e 10
• XL j6 XC -j2
• Z R (XLXC)
• theta angle(Z) 0.4636 pi
• 180 pi
• ----- ----
• theta_degree theta
• theta_degree (180theta)/pi
• 26.5615 degree 0.4636 pi
• mag_Z abs(Z)

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7-5 Special Variables and Constants (continue)

• Example 7-6
• MATLAB Program (cont.)
• RLC_1.m
• I e/Z
• I_thea_degree angle(I) (180)/pi
• I_mag abs(I)
• VR IR
• VL IXL
• VC IXC
• VR (VL VC) e 10 volt

• VR
• 8.0000 - 4.0000i
• VL
• 3.0000 6.0000i
• VC
• -1.0000 - 2.0000i
• gtgt VR (VL VC)
• ans
• 10

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Summary

• Managing Variables and Workspace
• MATLAB Commands for Working with Files and the
  Operating System
• Controlling Command Windows
• Date and Time Functions
• Special Variables and Constants

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Question?

• Answers
• Email linm_at_ipfw.edu