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Introduction to Variables and Arrays in MATLAB Programming

This lecture covers the fundamental concepts of variables and arrays in MATLAB. It explores how to assign values to variables, the rules for naming them, and the difference between mathematical and programming operations. Key topics include creating and manipulating arrays, using assignment statements, and understanding expressions, including mathematical sequences and operator precedence. Gain insights into the importance of meaningful variable names and how to effectively use MATLAB for computational tasks.

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Introduction to Variables and Arrays in MATLAB Programming

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  1. COMP 116: Introduction to Scientific Programming Lecture 3: Variables and Arrays

  2. Recap • You can use MATLAB as a calculator • Operators, math functions, etc. • 20 + 30, sin(pi/2), etc. • Assignment: • <variableName> = <expresssion> • x=3 • y=4 • z = sqrt( x^2 + y^2 )

  3. What is Assignment?<variableName> = <expression> • Assigning a value to a storage location in computer memory. • Variable name on left-hand side • Expression on right-hand side • Expression is evaluated and reduced to a single value • Value is stored in storage location associated with variable name

  4. Review • Variables • Arrays

  5. What is a Variable? • A user defined name to represent a piece of memory for storing evaluated value(s). • A variable consists of 5 items Name: Meaningful human readable name How the user refers to variable Value: Actual value associated with variable Stored in memory Data Type: How to interpret variable for data representation Size: How much storage memory is needed to store data value Can be inferred from data type Storage location: Usually hidden from user by the interpreter or compiler How the computer refers to a variable

  6. Mathematical statement vs. Programming command/definition • Consider the following two lines x = 1 x = x + 1 • What does the second statement mean? (a) Mathematically? • Makes no sense! (always false) (b) Programmatically? • Read value of x out of storage location • Add one to this value • Store new value back into x’s storage location • Decrement works the same way • x = x - 1

  7. <variableName> = <expresssion>

  8. Variable Naming RulesUse Valid Names • Length • 1 to 63 characters long • If you type more than 63 characters, the characters past 63 are ignored • namelengthmax for actual length • Syntax • Starts with a single letter followed by any number of letters, digits, or underscores. • Digits [0-9], Letters [a-z, A-Z], Underscore ‘_’ • No spaces allowed Often, use underscores (or CamelCase) instead of spaces: • life_the_universe_and_everything_else = 42; • lifeTheUniverseAndEverythingElse = 42;

  9. Naming Rules (contd.) • Avoid Keywords (if, else, while, for, …) • Result: Error • If in doubt, use iskeyword function • Avoid Function names (sin, abs, …) • Result: Hiding of useful functions • Use clear to eliminate problem names • Use which to find out if a variable name is already in use • Use meaningful names • currentStudent better than a, whateva, or currItem • Write readable names • currentStudent better than (cS, crSt, orcrrStdnt)

  10. <variableName> = <expresssion>

  11. What is an Expression? • A mathematical sequence of operators, functions, variables, numbers, and parenthesis that evaluates to a value • Examples: • 7 • 5*(4+3) • sin(2*pi) • sqrt(pi) + tan(exp(2)) - 7 • 23 + sqrt( -1 ) / (4 – 4i)

  12. Relational Operators • Type doc ops at prompt for more info • Useful for conditional logic in programming,

  13. Logical Operators • Type doc ops at prompt for more info • Useful for binary logic and expressions in programming,

  14. Operator Precedence (Full)

  15. Exercise • What do the following do: • x=2 • x=x^2+3 • x==8 • x==7 • x<9 • x>5 • y=(x<9) & (x>5)

  16. Review • Variables • Arrays

  17. Regular variables and array variables • Regular(scalar) variable x • Array(vector) variable y

  18. Creating array variables >> x=[5 3 2 11 6 5 2] >> x=[5, 3, 2, 11, 6, 5, 2] Using the colon operator >> x= -5:8 Random array >> x=rand(1,8)

  19. Array-Scalar arithmetic • x=[5 3 2 11 6 5 2] • x+2 • x*5 • y=x/5+2

  20. Array-Array arithmetic (use dot operator) • x= -5:8 • y= 7:20 Both arrays are the same size • x+ y • x .* y • z=x.*y + y +2

  21. Exercise: Solving math equations • Solve the MATH equation • (not a programming command) • Programming: >> x= -6:6 >> y=x.*x -6*x+8 find 0 in the y array >> plot(x,y)

  22. Practice • using assignment, variables, and expressions <variable> = <expression> • solving simple one variable equations using arrays

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