Introduction to MATLAB

1
Introduction to MATLAB

• Notes to complement on-line demo

2
MATLAB Overview

• What is MATLAB
• A program that may be used to automate
  mathematical computations
• Interpretive environment, calculations at the
  command line
• Includes scripting language, you can write
  programs
• Rich with engineering oriented functions
• Modern engineering tool widely used in
  engineering
• Includes Toolboxes for specialty applications
• Controls
• Signal Processing
• Bio-system simulation
• Includes block diagram based simulation
  Simulink

3
Simple Calculations

• Command Line Interpreter
• Set variables
• A3
• B3,4,7 row vector
• C3 4 7 column vector
• D1,23,4 matrix
• Show variables
• Who,whos
• Clear variables
• Clear, clear x
• Set iterated list
• E10.210 (start increment end)

4
Getting help

• Best
• Select Help from the menu (MATLAB 6)
• Next Best (UNIX/LINUX)
• Use the command HELP from the command prompt
• HELP Alone for general list topic areas
• Help topic for help on topic
• Topics are divided into general areas
• Controls, Signal processing, etc.
• Local functions may be added to the local dir
• Organized with
• General help
• Toolbox help

5
Complex Numbers

• Set number
• A3 4i
• Magnitude
• Mabs(A)
• Angle
• Alphaangle(A)
• Conjugate
• A_starconj(A)
• Imaginary part / real part
• Imag_a imag(A)
• Real_areal(A)
• Try sqrt(-1)

6
Simple Plotting

• Simple x/y plot
• x0120
• xsin(x)
• plot(x,y)
• Set line /point type
• plot(x,y,c) cyan points
• plot(x,y,c,x,y,y-) cyan points and yellow
  line
• Set Titles and labels Labels
• xlabel(X-axis), Ylabel(Y-Axis)
• Title(Title)
• Alternative Use figure menu /Edit/Axis
  Properties
• Set axis titles
• Main title
• Line properties etc.

7
3D plot

• Set x and y values
• x 0.120
• y 0.120
• Create matrices for xg yg grid
• xg, yg meshgrid(x,y)
• Calculate an equation for z on the grid
• z sin(pixg/20). sin(piyg/20)
• (note the . for element by element
  multiplication where xg and yg are 20x20
  matricies)
• Plot the surface or mesh
• surf(x,y,z) or mesh(x,y,z)

8
Matrix math

• Consider a set of equations
• Given x1,x2 you can find y1,y2.
• The more usual problem is y1,y2 are given and you
  need x1,x2
• Solution
• Write in matrix form and solve

9
Matrix math

• Example
• Set y,A
• Y 3 4
• A 7 , 4.5 3.3, 9.1
• Find A inverse (A-1)
• Ai inv(A)
• Calculate x
• x Aiy

10
Additional matrix operations

• Transpose a matrix
• (switch rows and columns)
• y y
• To multiply element by element by a scalar
• y sin(y) . y (replace each element by y sin
  y)

11
M-File -programs

• Use File menu to create or open a script file
• Use Matlab commands as script
• Save into m-file space and then execute by file
  name on the command line
• Example
• Save as sin_surf.m
• Execute as sin_surf on the command line

for i 130 for j 130 z(i,j)
sin(3.14159 ((i - 16) 2 (j - 16) 2) / (7
30)) ( j - 1) end end surfc(z)