MatlabIntro.ppt

1 MATLAB PRIMER by Michael Medvinsky(2014)

MATLAB MATLAB is a program for doing numerical computation. It was originally designed for solving linear algebra type problems using matrices. It’s name is derived from MATrix LABoratory. MATLAB has since been expanded and now has built- in functions for solving problems requiring data analysis, signal processing, optimization, and several other types of scientific computations. It also contains functions for 2-D and 3-D graphics and animation.

MATLAB When you first open MATLAB, notice: 1.The command window is where you'll give MATLAB its input and view its output. 2.The workspace shows you all of your current working variables and other objects. 3.The history shows you all commands you used in CW. 4.The Editor for MATLAB scripts (M-files) . To save & run the m-file type 'F5'. To open the editor with a new or old m-file use the command open file_name

MATLAB help For help, command description etc use F1 or following commands:  help command_name  helpwin command_name  doc command_name  helpdesk command_name  demo command_name  lookfor keyword (search unknown command) http://www.mathworks.com/support/ For example when running “help sin” one get SIN Sine of argument in radians. SIN(X) is the sine of the elements of X. See also ASIN, SIND. Overloaded functions Reference page in Help browser doc sin

Some Useful commands what List all m-files in current directory dir/ls List all files in current directory type test Display test.m in command window delete test Delete test.m cd/chdir Change directory pwd Show current directory which test Display directory path to ‘closest’ test.m who List known variables whos List known variables plus their size clear Clear variables from workspace clc Clear the command window

MATLAB & Matrices MATLAB treats all variables as matrices. For our purposes a matrix can be thought of as an array, in fact, that is how it is stored. Vectors are special forms of matrices and contain only one row OR one column. Scalars are matrices with only one row AND one column

Variable Names Variable names ARE case sensitive Variable names can contain up to 63 characters (as of MATLAB 6.5 and newer). One can use namelengthmax command to verify it. Variable names must start with a letter followed by letters, digits, and underscores. MATLAB variables are defined by assignment. There is no need to declare in advance the variables that we want to use or their type. Example x=1; % Define the scalar variable x y=[1 2 3] % row vector z=[1;2;3] % column vector A=[1 2 3;4 5 6;7 8 9] % 3x3 matrix whos % List of the variables defined Note: terminate statement with semicolon (;) to suppress output.

Special Variables ans Default variable name for results pi Value of π eps Smallest incremental number inf Infinity NaN Not a number e.g. 0/0 i,j,1i,1j imaginary unit i, i.e. square root of -1 realmin The smallest usable positive realnumber realmax The largest usable positive real number SpecialVars.m

Other symbols >> prompt . . . continue statement on next line , separate statements and data % start comment which ends at end of line ; (1) suppress output (2) used as a row separator in a matrix : specify range

Relational Operators MATLAB supports six relational operators. Less Than < Less Than or Equal <= Greater Than > Greater Than or Equal >= Equal To == Not Equal To ~=

Math & Assignment Operators Power ^ or .^ a^b or a.^b Multiplication * or .* a*b or a.*b Division / or ./ a/b or a./b or or . ba or b.a NOTE: 56/8 = 856 - (unary) + (unary) Addition + a + b Subtraction - a - b Assignment = a = b (assign b to a) Operators.m

MATLAB Logical Operators MATLAB supports five logical operators. not/~ element wise/scalar logical NOT and/& element wise logical AND or / | element wise logical OR && logical (short-circuit) AND || logical (short-circuit) AND

Logical Functions MATLAB also supports some logical functions.  xor (a, b) exclusive or  any(x) returns 1 if any element of x is nonzero  all(x) returns 1 if all elements of x are nonzero  isnan(x) returns 1 at each NaN in x  isinf(x) returns 1 at each infinity in x  finite(x) returns 1 at each finite value in x  find(x) find indices and values of non zero elements

Some Matrix functions zeros(rows, cols) – create zero matrix rand(rows, cols) – generate random matrix ones(rows, cols) – matrix with 1 in all entries eye (rows, cols) – identity matrix sub2ind, ind2sub indices manipulation

Extracting a Sub-Matrix A portion of a matrix can be extracted and stored in a smaller matrix by specifying the names of both matrices and the rows and columns to extract. The syntax is: sub_matrix = matrix ( r1 : rn , c1 : cn ) ; sub_matrix = matrix ( r1 : rn , : ) ; sub_matrix = matrix ( : , c1 : cn ) ; sub_matrix = matrix ( r1 : dr : rn , c1 : dc : cn ) ; where r1 and rn specify the beginning and ending rows and c1 and cn specify the beginning and ending columns to be extracted to make the new matrix. The terms dr and dc define spacing different than one. matrix.m

“Continuous” functions Numerically, we cannot represent a general continuous function (x,f(x)) because it requires handling infinite data (for each point in the range, we need to keep f(x)). Instead, we represent a function by its values at a finite number of data points (x_i,f(x_i)), where the series of points {x_i} is typically referred to as the sampling points or the grid points. Accordingly, the "continuous" functions in Matlab accepts a vector of point {x_i} and return a vector of values {f(x_i)}. Some functions  sqrt  log  cos/acos/sin/asin etc  exp - exponential  abs  sign  norm  sum  prod - product

Plotting MATLAB will plot one vector vs. another. The first one will be treated as the abscissa (or x) vector and the second as the ordinate (or y) vector. The vectors have to be the same length. MATLAB will also plot a vector vs. its own index. The index will be treated as the abscissa vector. Given a vector “time” and a vector “dist” we could say: >> plot (time, dist) % plotting versus time >> plot (time + i*dist) % plotting versus time >> plot (dist) % plotting versus index Sometime we want to see it with different colorline stile >> plot (time, dist, line_characteristics) And sometime we want to plot few functions in graphs >> plot(…), hold, plot(…) >> plot(t,d1,l_c1, t,d2, l_c2) To split page to several axes check use >> subplot (rows, cols, place)

Plotting There are commands in MATLAB to "annotate" a plot to put on axis labels, titles, and legends. For example: To put a label on the axes we would use: >> xlabel ('X-axis label') >> ylabel ('Y-axis label') To put a title on the plot, we would use: >> title ('Title of my plot') To distinct between function in the graph use: >> legend(legend_1, legend_2) plotting.m

Flow control (condition) An if - elseif - else structure. (Note that elseif is one word) if expression1 statements1 elseif expression2 statements2 else statements3 end An switch-case structure switch switch_expr case case_expr statement, ..., statement case {case_expr1, case_expr2, case_expr3, ...} statement, ..., statement otherwise statement, ..., statement end

Flow control (loops) A for loop in MATLAB for ind = 1:100 b(ind)=sin(ind/10) end Alternative (Most of the loops can be avoided!!!): x=0.1:0.1:10; b=sin(x); A while loop in while x <= 10 % execute these commands end

M-Files An M-file might be used as a script, i.e. file consist set of statements In additional, one use M-files to write function, in this case the file starts with function definition like: function y = f(x) function [u,v] = f(x,y,z) File name and the name of function in the file are usually identical, however while they are different, MATLAB use file name to call function. If you add additional function in same M-file, it considered sub-function and might be called from inside the M-file only. Only the first function might be called from outside.

Saving Results We can save all our results for future reference . The command diary ‘FileName' saves all output to command window into the FileName.txt file until this option is turned off by the command diary off The following commands save & load the entire workspace into the file 'MyMatFile.mat'  save 'MyMatFile'  load 'MyMatFile'  save 'x.mat' x % save a specific variable saving in ASCII format:  x = (-1:0.4:1)' ; y = sin(x*pi)  var = [x y] % double-column  save 'my_sin.dat' -ASCII -double var %Save in 16-digit ASCII format

MATLAB also have humor why % try this command

MatlabIntro.ppt

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MatlabIntro.ppt