 Chapter 2 MATLAB Fundamentals.

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Chapter 2 MATLAB Fundamentals

MATLAB Matrix Laboratory

Problem-Solving Methodology
H.C. Chen Problem-Solving Methodology State the problem clearly Describe the Input/Output (I/O) Work the problem by hand Algorithm - Numerical Method Develop a MATLAB Solution Debugging and Testing Documentation MATLAB Review

Why MATLAB? Industry standard software application
H.C. Chen Why MATLAB? Industry standard software application Wealth of built-in functions and libraries Toolboxes (add-on software modules) – image and signal processing, control systems design, fuzzy logic, etc. Has own structured programming language Ease of application and testing (pre- and post-processing without lots of programming and formatting) Platform independent MATLAB Review

MATLAB MATLAB is a numerical analysis system
Can write “programs”, but they are not formally compiled Should still use structured programming Should still use comments Comments are indicated by “%” at the beginning of the line

Program Documentation
Comments!!! You must include comments in the computer programs you turn in -- otherwise we will have great difficulty knowing what you are doing

For example, here is some cryptic code without comment
for j=0:2 k=(2-j)*(1+3*j)/2 end What does it do? Put a comment in % turns (0,1,2) into (1,2,0)

MATLAB Windows Command Window -- enter commands and data
-- print results Graphics Window -- display plots and graphs Edit Window -- create and modify m-files

Managing MATLAB Environment
who or whos -- See the current runtime environment clear -- remove all variables from memory clc clear the command window clf clear the graphics window save -- save the workspace environment load -- restore workspace from a disk file abort -- CTRL-C help -- help “command” Really good “help” command

MATLAB Syntax No complicated rules
Perhaps the most important thing to remember is semicolons (;) at the end of a line to suppress output Type “more on” to keep text from leaving screen too fast diary “filename” saves a text record of session diary off turns it off

MATLAB MATLAB’s basic component is a Vector or Matrix
Even single value variables (Scalars) All operations are optimized for vector use Loops run slower in MATLAB than in Fortran (not a vector operation) “size” command gives size of the matrix

Scalars, Vectors, Matrices
MATLAB treat variables as “matrices” Matrix (m  n) - a set of numbers arranged in rows (m) and columns (n) Scalar: 1  1 matrix Row Vector: 1  n matrix Column Vector: m  1 matrix

>> pi ans = 3.1416 >> size(pi) >> a=[1 2 3; 4 5 6] a = >> size(a) ans = a=

Complex variables MATLAB handles complex arithmetic automatically
No need to compute real and imaginary parts separately The unit imaginary number i = is preassigned » x=5+2*i x = i » y=5*x+3 y = i

MATLAB Example default filename filename “matrix1” » x=3+5-0.2 » who
7.8000 » y=3*x^2+5 y = » z=x*sqrt(y) z = » A=[1 2 3; 4 5 6] A = » b=[3;2;5] b = 3 2 5 » C=A*b C = 22 52 » who Your variables are: A b y C x z » whos Name Size Bytes Class A x double array C x double array b x double array x x double array y x double array z x double array » save Saving to: matlab.mat » save matrix1 default filename filename “matrix1”

Data types All numbers are double precision
Text is stored as arrays of characters You don’t have to declare the type of data (defined when running) MATLAB is case-sensitive!!!

Variable Names Usually, the name is identified with the problem
Variable names may consist of up to 31 characters Variable names may be alphabetic, digits, and the underscore character ( _ ) Variable names must start with a letter ABC, A1, C56, CVEN_302 day, year, iteration, max time, velocity, distance, area, density, pressure Time, TIME, time (case sensitive!!)

Initializing Variables
Explicitly list the values reads from a data file uses the colon (:) operator reads from the keyboard A = [1; 3; 5; 10]; B = [1 3 5; ] C = [ ; 0 1 … (continuation) 1 -2; ] E = [A; 1; A]; F = [C(2,3); A]

Matrix Concatenation

Colon Operator Creating new matrices from an existing matrix
F = C(:, 2:3) = [2,5; 0,1; 2,-1; 1,4]

Colon Operator Creating new matrices from an existing matrix
E = C(2:3,:) = [-1 0 1; ]

Colon Operator Creating new matrices from an existing matrix
G = C(3:4,1:2) = [3,2; 0,1]

Colon Operator Variable_name = a:step:b time = 0.0:0.5:2.5
Negative increment values = 10:-1:2 values = [10, 9, 8, 7, 6, 5, 4, 3, 2]

linspace Function linspace(x1, x2) gives 100 evenly spaced values between x1 and x2 x = linspace(x1,x2) linspace(a,b,n) generate n equally spaced points between a and b x = linspace(a,b,n) » linspace(0,2,11) ans = Columns 1 through 7 Columns 8 through 11

logspace Function logspace(a,b,n) generates a logarithmically equally spaced row vector x = logspace(a,b,n) logspace(a,b) generates 50 logarithmically equally spaced points x = logspace(a,b) » logspace(-4,2,7) ans =

Special Matrices

Scalar Arithmetic Operations
In order of priority (Matrix inverse) Example: x = (a + b*c)/d^2 count = count + 1

Order of Precedence of Arithmetic Operations
Parentheses, starting with the innermost pair Exponentiation, from left to right Multiplication and division with equal precedence, from left to right Addition and subtraction with equal precedence, from left to right Examples: factor = 1 + b/v + c/v^2 slope = (y2 - y1)/(x2 - x1) loss = f * length/dia * (1/2 * rho * v^2) func = *(3*x^4 + (x + 2/x)^2)

Order of Precedence of Arithmetic Operations
The priority order can be overridden with parentheses » a=3; b=5; c=2; » s1 = a-b*c s1 = -7 » s2=(a-b)*c s2 = -4 » y = -7.3^2 y = » y=(-7.3)^2 Multiplication has higher priority than subtraction Exponentiation has higher priority than negation

Array Operations An array operation is performed element-by-element
MATLAB: C = A.*B;

Element-by-Element Operations

Vector and Matrix operations
But a*b gives an error (undefined) because dimensions are incorrect. Need to use .*

Vectorized Matrix Operations

Array Operations for m  n Matrices

Matrix Transpose

Built-in Functions All the standard operators +, , *, /, ^
Sqrt( ), abs( ), sin( ), cos( ), exp( ), tanh( ), acos( ), log( ), log10( ), etc. These operators are vectorized

Built-in Functions Certain functions, such as exponential and square root, have matrix definition also Use “help expm” and “help sqrtm” for details >> A = [1 3 5; 2 4 6; ] A = >> B = sqrt(A) B = i i >> C = sqrtm(A) C = i i i i i i i i i (element by element) (C*C = A)

MATLAB Graphics One of the best things about MATLAB is interactive graphics “plot” is the one you will be using most often Many other 3D plotting functions -- plot3, mesh, surfc, etc. Use “help plot” for plotting options To get a new figure, use “figure” logarithmic plots available using semilogx, semilogy and loglog

Plotting Commands plot(x,y) defaults to a blue line
plot(x,y,’ro’) uses red circles plot(x,y,’m*’) uses magenta asterisks If you want to put two plots on the same graph, use “hold on” plot(a,b,’r:’) (red dotted line) hold on plot(a,c,’ko’) (black circles)

Free-Falling Bungee Jumper
Use built-in functions sqrt & tanh >> g = 9.81; m = 75.2; cd = 0.24; >> t = 0:1:20 t = Columns 1 through 15 Columns 16 through 21 >> v=sqrt(g*m/cd)*tanh(sqrt(g*cd/m)*t) v = Columns 1 through 9 Columns 10 through 18 Columns 19 through 21

Plot the velocity versus time curve
>> plot(t,v); grid on >> title('Free Falling Bungee Jumper') >> xlabel('time t (second)'); ylabel('velocity v (m/s)') >> print –djpeg bungee.jpg How to change line thickness, line color, font size, symbols, marker size, etc.?

Color, Symbols, and Line Types
Use “help plot” to find available Specifiers b blue point solid g green o circle : dotted r red x x-mark dashdot c cyan plus dashed m magenta * star y yellow s square k black d diamond v triangle (down) ^ triangle (up) < triangle (left) > triangle (right) p pentagram h hexagram Colors Symbols Line Types

Adjust line thickness, font size, marker size, etc.
» x=0:0.1:5; » y=2*x.^3-12*x.^2+8*x-6; » H=plot(x,y,'b',x,y,'r*'); » set(H,'LineWidth',3,'MarkerSize',12) » xlabel('x'); ylabel('y'); » title('f(x)=2x^3-12x^2+8x-6'); » print -djpeg075 poly.jpg Adjust line thickness, font size, marker size, etc. element-by-element operations x.^n

» x=0:0.1:10; » y=sin(2.*pi*x)+cos(pi*x); » H1=plot(x,y,'m'); set(H1,'LineWidth',3); hold on; » H2=plot(x,y,'bO'); set(H2,'LineWidth',3,'MarkerSize',10); hold off; » xlabel('x'); ylabel('y'); » title('y = sin(2\pix)+cos(\pix)'); » print -djpeg075 function.jpg

» x=0:0.1:3; y1=exp(-x); y2=sqrt(x);
» H=plot(x,y1,'b-',x,y2,'r--'); » set(H,'LineWidth',3) » xlabel('x'); ylabel('y'); title('MATLAB Plots'); » H1=text(1.8,0.2,'exp(-x)'); set(H1,'FontSize',18); » H2=text(1.8,1.3,'sqrt(x)'); set(H2,'FontSize',18);

figure or figure (#) : open a figure
Plotting Commands plot (x, y) plot(x1, y1, x2, y2) plot (x, y, ‘color symbol line style’) » x = linspace(0, 2*pi); » y = sin (2.*x); » z = cos (0.5*x); » plot (x, y) » plot (x, y, x, z) » figure (2) » plot (x, y, 'r o -'); grid on » hold on » plot (x, z, 'b * :') figure or figure (#) : open a figure (red, circle, solid line) (blue, star, dotted line)

Graphics Commands Axis, Labels, and Title
xlabel ( label ) ylabel ( label ) title ( title of the plot ) text ( x_location, y_location,  text  ) axis ( [ x_min x_max y_min y_max ] ) » xlabel (Time) » ylabel (Temperature) » title (Temperature Record : ) » text (17, 120, Record High ) » text (85, -40, Record Low ) » axis ([ ]) » hold off   - text string

CVEN 302-501 Homework No. 1 Chapter 2
Problems 2.2 (15), 2.4 (15), 2.7 (20), 2.10 (20), 2.11 (20). Due Friday. 09/05/2008 at the beginning of the period