CMPSC 200 Summarized Notes- Midterm

Computer

A programmable electronic device that can store, retrieve, and process data

MATLAB Stands for

Matrix Laboratory

Syntax error

Output when the computer does not understand the instruction

Logic error

Program input by the user is read properly by the computer but is not the intended output desired

CPU

Central processing unit

Arithmetic and Logic Unit (ALU)

Performs mathematical functions

Control Unit

Fetches the next instruction, decodes the instruction, and then executes the instruction as appropriate

Volatile memory

Temporary storage that is faster; examples include RAM and DRAM

Non-Volatile Memory

Permanent storage that is slower; examples include read-only memory (ROM), compact discs (CDs), and magnetic tape

Operating System (OS)

Software that allocates computer resources and allows communication between the user and the computer

Programming Language

A structured language that exists to communicate information to a computer in the form of a program

High-Level Languages

Easy for humans to understand, but too difficult for a computer to understand directly (e.g., C = A + B)

Low-Level Languages

Harder for humans to understand, but easier for a computer to convert to usable instructions (e.g., ADD A B C)

Machine Language

Binary digits (0s and 1s) containing instructions understood directly by the computer

Compiled Language

Code is reduced to machine-specific instructions prior to runtime and saved as an executable file; generally runs faster

Interpreted Language

Code written by the programmer is saved in the same format as it was originally written in, which is converted to machine-specific instructions at runtime. (e.g., MATLAB, Python)

Variable

Container for some information; must begin with a letter and can contain up to 63 characters

Assignment rule in MATLAB

Whatever happens on the right-hand side is stored into the variable on the left-hand side of the equals sign

Case sensitivity in MATLAB

MATLAB is case-sensitive, meaning uppercase and lowercase letters matter

clc

Clears the command window where outputs are displayed

clear

Clears the workspace and removes variables

Comments in MATLAB

Started with the % symbol and appear green; block comments use %{ and %}

Section break (Cell)

Created using %% to allow sections of code to be run independently

Order of operations

Parentheses, Exponents, Multiplication and Division, Addition and Subtraction

Element-by-element operation

Performed using a dot operator (e.g., .*) to multiply corresponding elements of matrices

Default values in MATLAB

pi, i, and j

Creating matrices/arrays

Rows are separated by semicolons (;) and columns are separated by spaces or commas (,)

Colon operator (1:5)

Stores values from a lower bound to an upper bound in steps of one (lower:step:upper)

abs()

Finds the absolute value of data or each item in an array

sqrt()

Calculates the square root for real and imaginary numbers

sign()

Finds if a number is positive, negative, or zero, displaying -1, 0, or 1

rem()

Finds the remainder of a division operation

log vs log10

log is the natural logarithm, while log10 is log base 10

Floor and Ceiling

floor rounds down and ceiling rounds up to the nearest integer

factor()

Lists the factors of a number

gcd() & lcm()

Finds the greatest common divisor and least common multiple of numbers

isprime()

Determines if a number is prime (returns 1 for true, 0 for false)

rats()

Converts the input to a fraction format

linspace(n,m,p)

MATLAB function that generates a row vector of linearly spaced points with a specified start, end, and number of points

subplot(m, n, p)

Splits the figure window into m rows and n columns, and selects the p-th slot counting row-by-row from top-left (this is ONLY for subplots other wise counting matrices is top to bottom, left to right)

Array storage order in MATLAB

MATLAB stores and reads matrices from top to bottom, then left to right (column dominant)

plot()

Plots y-data versus x-data

legend()

Creates a legend for a plot

comet()

Creates an animated plot

title()

Adds a title to a plot

figure()

Calls a figure window, needed to make a graph

clf

Clears the content of a figure window without deleting the window itself

close

Deletes one or more figure windows

axis()

Used to control the axes of a plot

semilogy() & loglog()

Plots normal y vs log x, and log y vs log x respectively

plot3() & surf()

Plots 3D line plots and 3D surface plots

Pass by value

The only way MATLAB passes data into functions

Function parts

1. Name

2. Inputs

3. Outputs

4. description comments

requires an end statement and must be saved in the active folder

Scope (Local vs Global)

Local variables exist only inside their function/workspace; global variables are visible and modifiable across multiple parts of code

Anonymous functions

Created using the @ symbol for quick, single-line functions without a separate .m file

input()

Requests input from the user; using 's' specifies a string input

disp()

Prints the contents of a variable to the screen without its label or formatting capabilities

num2str()

Converts a number input into a character array/string

fprintf()

Prints formatted output to the screen or a file using type fields

fprintf type field %f

Fixed-point notation

fprintf type field %e

Exponential notation

fprintf type field %d

Decimal notation; does not include trailing zeros if integer, or uses exponential notation if fractional

fprintf type field %i

Integer notation

fprintf type field %g

The shorter of %f or %e

fprintf type field %c

Character information (one character at a time)

fprintf type field %s

String of characters (displays entire string)

Formatting characters in fprintf

\n for a new line, \r for carriage return, \t for tab, and \b for backspace

ginput()

Used to get data points from a plot

dlmwrite()

Used to write delimited output

Sequence structure

Lines of code executed one after another

Selection structure

Enables branches within code based on conditions (true/false)

Repetition structure

Causes a group of statements to be executed multiple times (loops)

Pseudocode

Language-independent verbal description of computer code

Flowchart

Graphical representation of how code flows and progresses

find command

Finds the indices of elements in a matrix that meet a specific criteria

Relational Operators (==, ~=, ~)

Equality check, not equal to, and logical NOT

Logical Operators (&, |, &&, ||)

AND/OR for vectors, double opporators for scalars

xor()

Exclusive or logical operation

for loop

Used when you know exactly how many times you want to repeat an action

while loop

A pretest loop that executes as long as a specified condition remains true

For loop execution count

Runs a fixed number of times equal to the number of elements in the index matrix; can run 0 times if the index vector is empty

While loop execution count

Runs conditionally; can run 0 times (if the condition is initially false), a specific number of times, or infinitely (if the condition never becomes false)

break statement

Terminates the smallest enclosing for or while loop prematurely

continue statement

Skips the rest of the current loop iteration and advances to the next pass

Counter

A variable that keeps track of a parameter of interest (e.g., counting occurrences or accumulating sums)

Infinite loop

A loop that never terminates and runs continuously

Keyboard shortcut to stop infinite loops

Windows: Control-C; Mac: Command-Period

tic / toc

Stopwatch feature used to measure elapsed execution time in seconds

etime()

Performs a comparison between a start time and an end time (clock-based)

Pre-allocation

Allocating space for a vector or matrix beforehand (using zeros, ones, etc.) to significantly boost loop performance

Output suppression

Using a semicolon (;) at the end of statements inside loops to prevent printing every iteration and greatly improve speed

2 ways to print in MATLAB

disp( ) and fprintf( )

Types of Computer Code:

sequences, selection structures, repetition structures

Loops should be your first choice in matlab

NOOO, use a built-in function if available

Types of Loops for all computer languages

for, while, do while

Types of loops in MATLAB

for and while

Nesting for loops

the inner loop must fully execute before running the outer loop a second time

2 types of counters

how many (numbers in a data set meet a specification), how much (e.g. what is the sum of the numbers that meet the specification/)

T or F: Every for loop can be made into a while loop, but not every while loop can be made into a for loop

True, this is done by adding a counter to keep track of how many times a while loop has executed, and terminate once it has reached the desired number of interactions

4 Performances “Guiding Principles”

1. only print using print statements

2. pre-allocating vectors

3. use recommendations from MATLAB GUI

4. run code multiple times for average times