1 / 26

Introduction to Matlab

Introduction to Matlab. StatLab Workshop Yale University Maximiliano Appendino, Economics October 18 th , 2013. What is Matlab?. Matlab is a matrix-based tool for numerical computations Powerful Easy to use Programming language Interactive environment Lots of available toolboxes.

floyd
Download Presentation

Introduction to Matlab

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to Matlab StatLab Workshop Yale University Maximiliano Appendino, Economics October 18th, 2013

  2. What is Matlab? • Matlab is a matrix-based tool for numerical computations • Powerful • Easy to use • Programming language • Interactive environment • Lots of available toolboxes

  3. Getting Help • Useful links: http://statlab.stat.yale.edu/help/FAQ/matlab_FAQ.jsp • Mathworks' Getting Started • Matlab Center • Kermit Sigmon’s Matlab Primer • Many others • Google your question • Matlab’s help • Online • Statlab Consultants: Max Perez Leon, Zhentao Shi

  4. Acquiring Matlab • ITS Software Library & Resources: • http://www.yale.edu/its/software/ • Free for students: Matlab R2013a • Available in Statlab locations • The Center for Science and Social Science Information • 219 Prospect St, Basement • Kline Biology Tower • Rosenkranz Hall • 115 Prospect St, Room 01

  5. Launching Matlab • Double-click the “MATLAB R2013a” icon on the desktop • Or click the start bottom, type MATLAB and enter • Usual Interface: • Command Window • Workplace • .MAT files • Command history • Current Folder

  6. Interface • Can be used as a calculator • “help” gives you a list of all topics • “help topic” informs you about the particular topic • Example: >> help >> help stats >> help normcdf

  7. Entering Matrices • Entered manually: >> A = [1 2 3 4; 5 6 7 8; 9 10 11 12] • Generate it by built-in functions • Loaded from a file • .MAT or Menu File  Import Data…

  8. Matrix Operation • + addition • - subtraction • * multiplication • ^ power • ‘ transpose • Element-by-element: preceded the operators by . • Subscripts: >> B = A(2,3)

  9. Matrix Operation • Matrix Multiplication >> [1 2; 3 4]*[1 2; 3 4] [7 10; 15 22] • Element-by-element Multiplication >> [1 2; 3 4].*[1 2; 3 4] [1 4;9 16]

  10. The Colon Operator : • One of Matlab’s most important operators: • Portions of a matrix: >> C = A(:,3) >> D = A(1,:) >> E = A(1:2,1:3) • Create matrices using increments: >> F = [1:0.1:1.5]’ >> G = [1:0.1:1.5; 1:0.5:3.5]

  11. Matrix Generation Functions • Zeros: >> zeros(3,3) • Ones: >> ones(3,3) • Identity: >> eye(3) • More on matrices and linear algebra: >> help elmat >> help matfun

  12. Random Matrices • Pseudo-Random numbers: • Change the seed: >> rng('shuffle') >> rng(15) • U[0,1] random variable: >> RU = rand(3,4) • Normal random variable: >> RN = randn(4,3)

  13. Matrix manipulation • Concatenation: >> A2 = [A A.^2; A./2 A] • Deleting rows and columns: >> A2(:,7:8) = [] • Adding rows and columns: >> A2 = [1:2:11;A2] • Knowing the size: >> sizeA2 = size(A2)

  14. Suppressing Output • If you simply type a statement and press Enter Matlab automatically displays the results on the Command Window • If you end the line with a semicolon ; Matlab performs the computation but does not display any result >> H = rand(2,2) >> H = rand(2,2); >> H

  15. Functions • Matlab provides a large number of standard elementary mathematical functions: >> abs(-10) >> sqrt(9) >> x = [0:0.1:2*pi]; >> y = sin(y); • Look for the ones you need: • Google >> help

  16. Graphics • Matlab generate 2-dimensional plots easily: >> plot(x,y) >> y2 = y + 0.25; >> y3 = y + 0.50; >> plot(x,y,x,y2,x,y3) • With a friendly interface to edit them

  17. Graphics • Also 3-dimensional ones: • First we need to generate a grid: >> [X,Y] = meshgrid([-2:.2:2]); • Second we can calculate the function to graph: >> Z = X.*exp(-X.^2-Y.^2); • Finally the graph: >> surf(X,Y,Z)

  18. Programming • M-files contain Matlab code • .m is their extension • Matlab editor • Can be used as any command or function as long as they are in the “Current Folder” • Two types: • Scripts • Functions

  19. Scripts • A list of code grouped together • It does not accept argument or return output • Use them to register your work • Example: File  New Script disp(‘Hello’) File  Save  test.m >> test

  20. Functions • Functions are M-files that can accept input arguments and return output arguments. • The M-file and the function should have the same name • Example: function ar = area(radius) ar = pi*radius.^2; File  Save  area.m >> area(2)

  21. Flow Control • Matlab has the standard flow controls • If statements • For loops • While loops

  22. If statement a = 10; b = 11; if a > b disp('greater‘) elseif a < b disp('less‘) else disp('equal‘) end >> [a==b]

  23. For loops betavec = zeros(100,1); beta = 0.925; a = [1:100]; for i = 1:100 betavec(i)=beta^a(i); end plot(betavec) • But you should avoid for loops if possible: >> newbetavec=beta.^a

  24. While loops • The previous example would be: betavec = zeros(100,1); beta = 0.925; a = [1:100]; i = 1; while i < 101 betavec(i)=beta^a(i); i = i + 1; end plot(betavec)

  25. Solving problems • Check if somebody else has already solved it • Matlab itself • Anybody using Matlab • Solve it by yourself • Use Matlab’s matrix processing capacity as much as you can • Be organized with your code

  26. Thank you! Questions, Comments, Problems to solve?

More Related