Introduction to MATLAB

Transcription

1 Introduction to MATLAB

2 What you will learn The most important commands (from my view) Writing scripts (.m files) Defining MATLAB variables Matrix/array operations Importing and extracting data 2D plots Intro to statistic toolbox

3 Command window: enter the command/instruction Current folder: directory where we save our work (click browse button if you want to change) Workspace: Where our data is stored in MATLAB during the current session (will be removed if we close our current session) Command history: record commands entered in the command window

4 Scripts Script: A sequence of commands Use % to add comments for explanation/hints Save as an.m file (save before we run it, no space in the file name) Demo: Display the text finding nemo (use the command disp to display strings) Demo: x=5; y=x^3; z=x+y; calculate z

5 What we do if we are stuck: Use help! (The blue question mark on the top row) Use the command doc to get detailed information about the command.

6 Variables Variables are places to store data To create a variable, simply assign a value (on the right) to a name (on the left): A=3.14 B= nemo First character of a variable s name must be a LETTER; after that, any combination of letters, numbers and _ CASE SENSITIVE! (Nemo is different from nemo) Some names for variables are reserved:

7 Do it together Write a script with three MATLAB variables a=3.14; b='nemo'; c=5*2+1 Save the script and the variables Script will show up in the current folder as.m; variables as.mat How about do the following commands: 1+1=a, a=b=1

8 Vectors as MATLAB variables x=1:1:5 y=linspace(1,5,5) Use ; to suppress output line (save space!) Imagine if you are writing x=1:0.1:1000, what would happen if you don t put the ;

9 Matrices as MATLAB variables Let s create a 2*3 matrix: You can also use : to do the matrix above

10 Matrix operation vs. Array operation Matrix operation (standard mathematical way): Inner dimension must agree (number of columns of A=number of rows in B) Array operation: element wise Two matrices: same shape and size Use dot (.) before the operator.*./.^

11 Let s try two types operations First, create matrices A and B.

12 Creating variables by importing external data (e.g., text file, spreadsheet) Use Import Wizard 1. Select file to be imported in the current folder. Right click on it and select import data. 2. If we do that correctly, it will show up in the workspace window. Instead of using Import Wizard, you can also import data programmatically by using the command import. Use doc for details

13 Do the cherry picking Extract data: 1. Double click on the variable (large dataset) in the workspace window 2. Highlight the area to extract 3. Right click and select create variable from selection 4. Rename the new variable 5. Right click on the variable on the workspace and save it to the current folder Example: Seattle and Houston rainfall data

14 Plot Method 1: use command plot Use doc plot to see the syntax of plot Method 2: use interactive plotting tool. Hold control and select the variables in work space, then click on the plot button Then use plottools command for plot editing

15 Statistics toolbox Mean and standard deviation command m = mean(x); s = std(x) ph in Lake Washington example Use cdfplot to display the plot of the cumulative distribution function (cdf) for the data Use dfittool to fit the data

16 Enjoy your homework