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Introduction to MATLAB

Introduction to MATLAB. Alternative MATLAB Introduction Lecture authored by Annie Abell. Introduction to MATLAB. MATLAB is a powerful program for numerical computations, plotting and programming . Use it as a calculator. Define variables and use them in calculations.

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Introduction to MATLAB

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  1. Introduction to MATLAB Alternative MATLAB Introduction Lecture authored by Annie Abell

  2. Introduction to MATLAB MATLAB is a powerful program for numerical computations, plotting and programming. • Use it as a calculator. • Define variables and use them in calculations. • Use built-in functions. • Plot graphs. • Write and run computer programs. • Perform symbolic mathematics.

  3. Open MATLAB now: Click on the shortcut icon or select: start / All programs / MATLAB There will be a fairly long initialization process, then following prompt should appear in the command window: >>

  4. Command prompt Workspace (variable values) Current Directory (lists file, etc.) Command History (what has been typed) Command Window (where commands are entered)

  5. MATLAB’s Working Directory When you first start MATLAB it is a good practice to change the working directory to your Z: drive or USB device. Keep all of your files in the same folder so you do not have to constantly change your directory

  6. Order of Precedence Higher-precedence operations are executed before lower-precedence operations (like Excel or graphing calculators). If two operations have the same precedence, then the expression is executed from left to right. PRECEDENCEOPERATION First Parentheses (innermost pair first) Second Exponentiation. Third Multiplication and division Fourth Addition and subtraction

  7. Precedence of Operations Task : Find the average of 7 and 8 >> (7+8)/2 ans = 7.500 … correct!  >> 7 + 8 / 2 ans = 11 …not what we wanted 

  8. Precedence of Operations Task: Add the cube root of 27 to the 5th root of 32 >> 27 ^ 1/3 + 32 ^ 0.2 ans = 11 … not what we wanted  >> 27 ^ (1/3) + 32 ^ 0.2 ans = 5

  9. Variable Definition >> x = 5 x = 5 >> x = x + 5 x = 10 This statement does not make any mathematical sense but in programming language it changes the value of ‘x’ to a new value.

  10. Calculations with Variables We can use the variables defined previously to do calculations. Define the following: a=8, my_var =12 >> a + my_var ans = 20 >> a * my_var^2 ans = 1152

  11. Rules About Variable Names • Can be up to 63 characters long. • Must begin with a letter. • Can contain letters, digits, and the underscore character (no spaces). • MATLAB is case sensitive; it distinguishes between uppercase and lowercase letters. • Avoid naming variables with names that are used by MATLAB: exp, sin, cos, sqrt, length, mean, max, min…

  12. Examples of Variable Names Acceptable: My_name MyName myname1 Unacceptable: 1Name starts with numeral My Name spaces not allowed My-Name special characters not allowed

  13. Built-In Math Functions: Examples exp(x) exponential (ex) log(x)natural logarithm (log base 'e') log10(x)base 10 logarithm (log) sqrt(x) square root abs(x) absolute value

  14. Built-In Math Functions In MATLAB, trigonometric functions use radians. So for these examples, x is in radians: • sin(x), cos(x), asin(x), acos(x), tan(x), cot(x) MATLAB also has equivalent functions where x is in degrees: • sind(x), cosd(x), tand(x), etc

  15. Built-In Math Functions: Examples Task: calculate sin(∏/ 2). Note: ∏ is defined by MATLAB as pi. >> sin(pi/2) ans = 1

  16. Built-In Math Functions: Examples Task: calculate e2 >> e ^ 2 ??? Undefined function or variable 'e' How do we fix this? >> exp(2) ans = 7.3891

  17. Built-In Math Functions: Examples Task: calculate sin2x, where x = ∏/4 >> x = pi/4 x = 0.7854 >>sin(2*x) ans = 1

  18. Built-In Math Functions: Examples Task: Using (cos2xsin2x + tan(x/2)) / e3x , find the value for x = 30 degrees. >> x = 30 x = 30 >> x = x * pi / 180 x = 0.5236

  19. Built-In Math Functions: Examples Task: Using (cos2x sin2x + tan(x/2)) / e3x , find the value for x = 30 degrees. >> (cos(2*x)* sin(x)^2 + tan(x/2)) / exp(3*x) ans = 0.0817

  20. Saving a Script File • Once the script file is completed, it must be saved. In our class use Save As to your Z:\ or your own USB drive. • This should be the same as the working directory you specified when you started MATLAB. • ALWAYS SAVE YOUR WORK. Back it up in multiple places for safety! To the cloud!!

  21. Saving a Script File Valid File Names • Prob1a.m • Prob1a.m • problemone.m Invalid File Names Prob-1a.m Special Characters not allowed Prob 1a.m Spaces not allowed 1aProb.m Cannot start with number

  22. Useful Programming Commands To clear the command window: clc >> clc To clear all variables previously defined: clear >> x = 5 x = 5 >> clear >> x ??? Undefined function or variable 'x'

  23. The Display Function: disp() This function displays a message to the command window. It can be a string of text or variablecontents. To display your message as text,use single quotes around your message: >> disp(‘Brutus Buckeye’) Brutus Buckeye

  24. The Display Function: disp() To display any variable contents, do not use quotes: >> x = 5 x = 5 >> disp(x) x = 5

  25. Suppressing Output This is good practice! You don't need all of your program displayed in the command window, just the relevant info. >> x = 6 x = 6 >> y = 7; …what happens when you type this?

  26. Script File Example Pythagoras' Theorem: Hypotenuse2 = Height2 + Base2 • Create a script file and name it Pyth.m • Clear the command window • Clear all variables from memory • Display your name and seat number • Declare height of triangle as 3 units • Declare base of triangle as 4 units • Find the hypotenuse of the triangle Hypotenuse Height Base

  27. How To Turn In All Assignments You must print two things for every MATLAB assignment: • Script file • Command window output … if you do not turn in both, you will lose points 

  28. Example Script File Printout Example Command Window Printout

  29. Self Check… Do you understand these concepts? • Arithmetic Operations with scalars: 5+3, 5*3 , 5^3 • Precedence of operations: 7+8/2 vs. (7+8)/2 • Variable assignment: a=8, b=12 • Calculations with variables: a+b, a*b • Important commands: clc, clear • Use of semi colons (;) to suppress output • Display function: disp(‘Brutus Buckeye’) • Mathematical functions: sin(pi/2) , exp(2) • Calculate the value of (cos2xsinx + tan(x/2)) / exp(3x) for x = 30 degrees

  30. Homework Assignment MAT-01 Introduction to Matlab

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