Notes, summaries, assignments, exams, and problems for Computers

SOFTWARE TESTING

Testing can only show the presence of errors, not their absence. The goal of testing is confidence.

• Validation: Are we building the right product? What does the customer need?
• Verification: Are we building the product right? Functional/Non-Functional requirements.

SOFTWARE INSPECTION VS. SOFTWARE TESTING

While inspection will go through the code without running the program, testing will run the program and look at the results. Incomplete programs can only be inspected, not tested. Inspections can control aspects of good software (maintainability…), not just the results.

TEST CASE:

• Requirements
• Data/Input
• Actions
• Expected Results

TEST CASE PRINCIPLES:

• A test tries to find flaws in a program.
• A good test case will show a possible defect

Optimization Problem and LP Relaxation

The objective function for an optimization problem is: Min 3x – 2y, with constraints x ≥ 0, y ≥ 0. x and y must be integers. Suppose that the integer restriction on the variables is removed. If so, this would be a familiar two-variable linear program; however, it would also be an example of an LP relaxation of the integer linear program.

Integers in Linear Programs

Integers cannot be used in linear programs.

• False

Simple Linear Regression Model

In a simple linear regression model, y = b0 + b1x + eb1, b1 represents the intercept.

Time Series Recurring Pattern

A time series that shows a recurring pattern over one year or less is said to follow a cyclical pattern.

Binary Integer Program Variables

In binary integer... Continue reading "Fundamentals of Optimization and Statistical Modeling" »

EXT2018.OA´WOMEN REALLY´

1.a-P1: A recent study found that women tend to live longer than men. b-P3: The academics also discovered that women have a stronger immune system.

• a-harsh
• b-hardship
• c-underpinnings
• d-outlive

4.p1: Danish researchers analyzed 19th-century data. p2: Research showed that women outlive men. p3: Males have a higher mortality rate even if...

ORD2018.OB·`Shop hires...`

1.a-P2: But it is important for businesses to understand their customers. b-P4: We thought it was an emotional and exciting experience.

• a-actually
• b-aware
• c-stressful
• d-understanding

4.p1: At the shop, Fabio performed. p2: When Fabio, the staff. p3: The staff had become...

ORD2017.OB`The victorian...`

1.a-P2: People would gather to observe. b-P3: The tableaus were a frozen... Continue reading "Gender Disparities in Mortality Rates and Immune System Function" »

Linux Memory Management

There are two components to memory management under Linux. First, the physical memory-management system deals with allocating and freeing pages, groups of pages, and small blocks of memory. The second component handles virtual memory, which is memory mapped into the address space of running processes.

Management of Physical Memory

The primary physical memory manager in the Linux kernel is the page allocator. This allocator is responsible for allocating and freeing all physical pages, and is capable of allocating ranges of physically contiguous pages on request. The allocator uses the buddy heap algorithm to keep track of available physical pages. A buddy-heap allocator pairs adjacent units of allocatable together; hence... Continue reading "Linux Memory Management and Scheduling Objectives" »

SIGNAL

SIGNAL: electromagnetic field which, thanks to its variations, is able to convey information from one place to another. It can be ANALOGUE (continuous) or DIGITAL (sequence).

MODULATION: the process of varying a periodic signal (car: constant amplitude and frequency) to use it for conveying some information. It can be done through AMPLITUDE (amplitude of carrier modified according to changes on modulating signal), FREQUENCY (frequency of carrier modified according to changes on modulating signal), or PHASE (phase of carrier is...). The transmitted modulated signal uses a frequency band around the carrier frequency. Reasons to use modulation: No signal mixing, long communication range, reduced antenna size.

ATTENUATION: As a signal propagates... Continue reading "Signal, Modulation, Attenuation, and Multiplexing in Communication Systems" »

A database management system contains

HARDWARE- Are the physical part of the computer: both the box and the internal components and the elements connected to it.

MOTHERBOARD-

Is the largest card with a printed circuit you see when you open a computer. All the other computer components are inserted on it, includes connectors or communication ports with peripherals and can also incorporate video, audio, and network devices.

MICROPROCESSOR-

Is the most important part of a computer. It is responsible for processing data, performing arithmetical-logical operations, and controlling all the other devices. It is characterized by its working frequency, measured in hertz, which determines its operating speed.

USB-

Universal serial bus, permits interconnection with practically any device. Standard... Continue reading "Hardware: The Physical Components of a Computer" »

Computer Networks

What is a Network?

A network is a number of computers linked together to allow the sharing of resources. A server usually provides services like file storage and email.

Types of Networks

There are two main types of networks:

• Local Area Network (LAN): A LAN covers a small area, such as a home or office.
• Wide Area Network (WAN): A WAN covers a large geographical area. Most WANs are made from several LANs connected together. WANs can be connected together using the internet.

Email

There are two main types of email:

• Client-based email: Often used by business users, client-based email involves downloading email from a server to an application on the user's computer.
• Webmail: Accessed through a web browser, webmail can be accessed from any

Servers

A server stores data to be used by other computers on a network. A server could be a specialized machine, or it can be a normal PC running server software. The server stores data and responds to requests for data or files, such as web pages.

Types of Server

There are many different types of servers. Some popular examples follow.

Web Servers

Web servers host websites and generally handle requests for static information such as HTML pages or images. They are used to manage the website on the server and often include FTP software, which can easily host and share large files. The Apache web server is a popular type of open-source web server software.

Application Servers

Many websites are classed as web applications, which contain programming and... Continue reading "Introduction to Computer Networks" »