MatLAB Lesson 1 : Overview & Environment

MatLABLesson 1 : Overview & Environment Edward Cheung email: icec@polyu.edu.hk Room W311g

Introduction • MatLAB stands for Matrix Laboratory • A Scientific calculator • A programming language • Good in Matrix calculation and graph plotting • written in Fortran and rewritten in C • common programming languages in Science & Engineering • MatLAB becomes a standard tool for scientists & engineers • Other computational tools; Maple, Mathematica, MathCad • Only Minor change since MatLAB 6 • Latest version is MatLab ver.7 (R2008a/b)

What we’ll cover?

Start Up – UI, Windows & Environment • Interactive, interpretative & programmable • Command, command history & workspace window • Transfer any command from the command history window to the command window by double clicking (also executes the command) or by click & drag • Launch Pad shows all available products and launch them • Workspace window keep track the variables defined in the programme • MatLAB 7 provided more information on variable like size, bytes, Max, Min, etc. in addition to Name, Value and Class (right click at the Workspace Browser) • The default data type use in calculation is double precision floating point numbers

Workspace Browser • Data is not save on exit unless execute “save Workspace As” from the File Menu • Or using the save function to save all to a MAT-file >>save % by default, stores all workspace variables in a binary format in the current directory in a file named matlab.mat • Can also save in ASCII format (readable but larger in size) >> Save filename.dat {variables} –ascii >> help save

Some keys • Arrow key to run previous command • clear screen of command window while keeping history >> clc >> clear % delete all variables • Command History Window can be cleared from Edit Menu • Who & whos • give variable information in the command window • Double clicking on a variable listed in the workspace window launches a document window called • the array editor • A semicolon (;) at the end of a command will suppress the output, try >>x=9; x=x+9

Keywords • You can redefine keywords >iskeyword % list reserved names • You can redefine function as variables • Example >> sin=3; >> sin(90) ??? Index exceeds matrix dimensions. >> which sin % check if sin is a function sin is a variable. >> clear sin % reset sin back to a function >> which sin % check again sin is a built-in function. • Most easy overlook is redefining i & j

Helpful Commands >> Help % give help topics >> Lookfor %Search all M-files for keyword • Try >> help format >> format compact % no linefeed >> format loose % default with linefeed >> format long % fixed-pt 15 digits >> format rat % rational format >> format blank % 2 decimal places • e.g. Get pi with the above format • No matter what format is selected, calculation are performed using double precision floating point numbers. >> format % reset to format default

Variables • Variables are created with >> variable = expression • Type of variables • Scalars • Vectors • Matrices • Strings

Variables • All name must starts with a letter • No special character except underscore, case sensitive X≠x • Convention – lowercase for variable & uppercase for constants but there are exceptions (eg speed of light=c) • MatLab 6 max length 31 characters • Namelengthmax = 63 (ver. 7function) • isvariablename – check the validity of variable name (boolean T=1; F=0), for example:- >> isvarname polyu >> isvarname poly-u >> isvarname poly_u

Scalar Variables • A variable with one row and one column • Creating scalars >> A=1; %creates a scaler >> B=1:10; % creates a vector >> C=[1,2;3,4]; creates a 2D matrix • end can be use to terminate a function or indicate last array index >> iskeyword end ans = 1 >> x=[2 3 4]; >> x(end+2)=7 x = 2 3 4 0 7

Scalar Operations >> x=5; >> y=3; >> z=x+y; >> s=x-y; >> a=x*y; >> d=x/y; >> d=y\x; >> p=x^y;

Vector • A vector can be a column matrix (nx1)or row matrix (1xn) • Helpful function in vector creation • Ones() & Zeros() >> x=ones(1,5) x = 1 1 1 1 1 >> x=zeros(5,1) x = 0 0 0 0 0

Create vector with scaling between elements >> x=linspace(1,5,5) x = 1 2 3 4 5 >> y=logspace(1,5,5) y = 10 100 1000 10000 100000 >> y(3) % addressing vector elements ans = 1000 >> x(7)=-9 % increase the size of a vector x = 1 2 3 4 5 0 -9 Array operators: Dot multiply or dot star .* -array multiplication dot divide or dot slash ./ -array division Dot power or dot caret .^ -array power

The colon operator • Create vector from a matrix >>x= xbegin:dx:xend Xbegin & xend = begin & end value of x dx = optional increment (default is 1) • Example:- >> x=1.1:5.1 x = 1.1000 2.1000 3.1000 4.1000 5.1000 • Transpose operator creates a column vector >> x=(1:5)' x = 1 2 3 4 5 >> b=0:2:10 % a vector starts at 0 ended at 10 with an increment 2

Matrices • In MatLab, a matrix is a variable with more than 1 row and 1 column • Variables with a dimension 1x1 is a scalar • Example:- create a 2x2 matrix and assigned to variable A >> A=[1 2;3 4] A = 1 2 3 4 (looks like a table) >> A=[1 2 3;4 5 6;7 8 9] A = 1 2 3 4 5 6 7 8 9 >> A(2,3) ans = 6

Matrix Sum >> lookfor sum TRACE Sum of diagonal elements. CUMSUM Cumulative sum of elements. SUM Sum of elements. SUMMER Shades of green and yellow colormap. ………. >> help sum SUM Sum of elements. For vectors, SUM(X) is the sum of the elements of X. For matrices, SUM(X) is a row vector with the sum over each column. ………

String >> a='polyu'; >> b=' '; >> c='ic'; >> [a b c] ans = polyu ic >> disp(a) polyu >> % display array >> disp('Solution 1.1') Solution 1.1

MatLab File Types • M-file • plain ASCII text that is interpreted at run time • parsed once and "just-in-time" compiled • best for development as well as platform independency • File Menu  New  M-file • % = comment statement >> what % give M-files & Mat files in current directory • Filename restriction • No special character including space except underscore ‘_’

MatLab File Types • Pcode file • a preparsed and encoded version of the M-file • Fast function load time; for large file, this is important • hide the source code from others. • Cannot convert Pcode back to the M-file source • Pcode is also platform independent • MEX file • native C or C++ files that are dynamically linked directly into the MATLAB application at runtime. • Need to be compiled for different system hardware • Fastest runtime but can crash the MatLab application

MatLAB Lesson 1 : Overview & Environment