Tài liệu PDF Economic Systems

Tài liệu PDF Economic Systems tài liệu, giáo án, bài giảng , luận văn, luận án, đồ án, bài tập lớn về tất cả các lĩnh vự...

Sự thiển cận trong Marketing Realtime Operating Systems Concepts and Implementation of Microkernels for Embedded Systems Dr. Jürgen Sauermann, Melanie Thelen 2 Contents List of Figures .v List of Tables .vi Preface 1 1 Requirements 3 1.1 General Requirements .3 1.2 Memory Requirements 3 1.3 Performance .4 1.4 Portability 5 2 Concepts .7 2.1 Specification and Execution of Programs 7 2.1.1 Compiling and Linking .7 2.2 Loading and Execution of Programs .11 2.3 Preemptive Multitasking 12 2.3.1 Duplication of Hardware .12 2.3.2 Task Switch .14 2.3.3 Task Control Blocks 16 2.3.4 De-Scheduling .19 2.4 Semaphores .21 2.5 Queues .26 2.5.1 Ring Buffers 26 2.5.2 Ring Buffer with Get Semaphore 28 2.5.3 Ring Buffer with Put Semaphore 29 2.5.4 Ring Buffer with Get and Put Semaphores .30 3 Kernel Implementation .33 3.1 Kernel Architecture .33 3.2 Hardware Model 34 3.2.1 Processor .34 3.2.2 Memory Map .35 3.2.3 Peripherals .35 3.2.4 Interrupt Assignment .36 3.2.5 Data Bus Usage .36 3.3 Task Switching 39 3.4 Semaphores .46 3.4.1 Semaphore Constructors 46 ii 3.4.2 Semaphore Destructor .46 3.4.3 Semaphore P() .46 3.4.4 Semaphore Poll() .48 3.4.5 Semaphore V() 49 3.5 Queues .51 3.5.1 Ring Buffer Constructor and Destructor .51 3.5.2 RingBuffer Member Functions 52 3.5.3 Queue Put and Get Functions 53 3.5.4 Queue Put and Get Without Disabling Interrupts 53 3.6 Interprocess Communication .54 3.7 Serial Input and Output .59 3.7.1 Channel Numbers 62 3.7.2 SerialIn and SerialOut Classes and Constructors/Destructors 63 3.7.3 Public SerialOut Member Functions .65 3.7.4 Public SerialIn Member Functions 69 3.8 Interrupt Processing .71 3.8.1 Hardware Initialization 71 3.8.2 Interrupt Service Routine 73 3.9 Memory Management .77 3.10 Miscellaneous Functions Economic Systems Economic Systems Bởi: OpenStaxCollege Vladimir Ilyich Lenin was one of the founders of Russian communism J.P Morgan was one of the most influential capitalists in history They have very different views on how economies should be run (Photos (a) and (b) courtesy of Wikimedia Commons) The dominant economic systems of the modern era have been capitalism and socialism, and there have been many variations of each system across the globe Countries have switched systems as their rulers and economic fortunes have changed For example, Russia has been transitioning to a market-based economy since the fall of communism in that region of the world Vietnam, where the economy was devastated by the Vietnam War, restructured to a state-run economy in response, and more recently has been moving toward a socialist-style market economy In the past, other economic systems reflected the societies that formed them Many of these earlier systems lasted centuries These changes in economies raise many questions for sociologists What are these older economic systems? How did they develop? Why did they fade away? What are the similarities and differences between older economic systems and modern ones? 1/22 Economic Systems Economics of Agricultural, Industrial, and Postindustrial Societies In an agricultural economy, crops are the most important commodity In a postindustrial society, the most valuable resource is information (Photo (a) courtesy Wikimedia Commons; Photo (b) courtesy AntanaBhadraLamichhane/flickr) Our earliest ancestors lived as hunter-gatherers Small groups of extended families roamed from place to place looking for means to subsist They would settle in an area for a brief time when there were abundant resources They hunted animals for their meat and gathered wild fruits, vegetables, and cereals They ate what they caught or gathered as soon as possible because they had no way of preserving or transporting it Once the resources of an area ran low, the group had to move on, and everything they owned had to travel with them Food reserves only consisted of what they could carry Many sociologists contend that hunter-gatherers did not have a true economy because groups did not typically trade with other groups due to the scarcity of goods The Agricultural Revolution The first true economies arrived when people started raising crops and domesticating animals Although there is still a great deal of disagreement among archeologists as to the exact timeline, research indicates that agriculture began independently and at different times in several places around the world The earliest agriculture was in the Fertile Crescent in the Middle East around 11,000–10,000 years ago Next were the valleys of the Indus, Yangtze, and Yellow rivers in India and China, between 10,000 and 9,000 years ago The people living in the highlands of New Guinea developed 2/22 Economic Systems agriculture between 9,000 and 6,000 years ago, while people were farming in SubSaharan Africa between 5,000 and 4,000 years ago Agriculture developed later in the western hemisphere, arising in what would become the eastern United States, central Mexico, and northern South America between 5,000 and 3,000 years ago (Diamond 2003) Agricultural practices have emerged in different societies at different times (Information courtesy of Wikimedia Commons) Agriculture began with the simplest of technologies—for example, a pointed stick to break up the soil—but really took off when people harnessed animals to pull an even more efficient tool for the same task: a plow With this new technology, one family could grow enough crops not only to feed themselves but others as well Knowing there would be abundant food each year as long as crops were tended led people to abandon the nomadic life of hunter-gatherers and settle down to farm The improved efficiency in food production meant that not everyone had to toil all day in the fields As agriculture grew, new jobs emerged, along with new technologies Excess crops needed to be stored, processed, protected, and transported Farming equipment and irrigation systems needed to be built and maintained Wild animals needed to be domesticated and herds shepherded Economies begin to develop because people now had goods and services to trade As more people specialized in nonfarming jobs, villages grew into towns and then into cities Urban areas created the need for administrators and public servants Disputes over ownership, payments, debts, compensation for damages, and the like led to the need for laws and courts—and the judges, clerks, lawyers, and police who administered and enforced those laws At first, most goods and services were traded as gifts or through bartering between small social groups (Mauss 1922) Exchanging one form of goods or services for another was known as bartering This system only works when one person happens to have something the other person needs at the same time To solve this problem, people ... in a computer system. Hardware and software cooperate in a computer system to accomplish complex tasks. The nature of that cooperation and the purpose of various hardware components are important prerequisites to the study of software develop- ment. Furthermore, computer networks have revolutionized the manner in which computers are used, and they now play a key role in even basic software development. This chapter explores a broad range of com- puting issues, laying the founda- tion for the study of software development. ◗ Describe the relationship between hardware and software. ◗ Define various types of software and how they are used. ◗ Identify the core hardware compo- nents of a computer and explain their purposes. ◗ Explain how the hardware compo- nents interact to execute programs and manage data. ◗ Describe how computers are con- nected together into networks to share information. ◗ Explain the impact and significance of the Internet and the World Wide Web. ◗ Introduce the Java programming language. ◗ Describe the steps involved in pro- gram compilation and execution. ◗ Introduce graphics and their repre- sentations. chapter objectives This book is about writing well-designed software. To understand software, we must first have a fundamental understanding of its role 1 computer systems 2 CHAPTER 1 computer systems 1.0 introduction We begin our exploration of computer systems with an overview of computer processing, defining some fundamental terminology and showing how the key pieces of a computer system interact. basic computer processing A computer system is made up of hardware and software. The hardware compo- nents of a computer system are the physical, tangible pieces that support the com- puting effort. They include chips, boxes, wires, keyboards, speakers, disks, cables, plugs, printers, mice, monitors, and so on. If you can physically touch it and it can be considered part of a computer system, then it is computer hardware. The hardware components of a computer are essentially useless without instructions to tell them what to do. A program is a series of instructions that the hardware executes one after another. Software consists of programs and the data those programs use. Software is the intangible counterpart to the physical hardware components. Together they form a tool that we can use to solve problems. The key hardware components in a computer system are: ◗ central processing unit (CPU) ◗ input/output (I/O) devices ◗ main memory ◗ secondary memory devices Each of these hardware components is described in detail in the next section. For now, let’s simply examine their basic roles. The central processing unit (CPU) is the device that executes the individual commands of a program. Input/output (I/O) devices, such as the keyboard, mouse, and monitor, allow a human being to interact with the computer. Programs and data are held in storage devices called memory, which fall into two categories: main memory and secondary memory. Main memory is the stor- age device that holds the software while it is being processed by the CPU. Secondary memory devices store software in a relatively permanent manner. The most important secondary memory device of a typical computer system is the hard disk that resides inside the main computer box. A floppy disk is similar to a hard disk, but it cannot store nearly as much information as a hard disk. Floppy A computer system page 0 A C + B C * B B T1 ST2 A⋅= T1 T2 T3 T4 ST1 ST2 ST3 FS = first scan ST1 ST1 T1+()T2⋅ FS+= ST2 ST2 T2 T3++()T1 T4⋅⋅= ST3 ST3 T4 T1⋅+()T3⋅= T2 ST1 B⋅= T3 ST3 CB⋅()⋅= T4 ST2 CB+()⋅= ST2 A ST1 B ST3 C B T1 T2 T3 T4 ST2 C B ST1 T2 ST1 T1 first scan ST2 T1 ST2 T2 T3 ST3 T3 ST3 T4 T4 T1 Automating Manufacturing Systems with PLCs (Version 4.2, April 3, 2003) Hugh Jack page i Copyright (c) 1993-2003 Hugh Jack (jackh@gvsu.edu). Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". This document is provided as-is with no warranty, implied or otherwise. There have been attempts to eliminate errors from this document, but there is no doubt that errors remain. As a result, the author does not assume any responsibility for errors and omissions, or damages resulting from the use of the information pro- vided. Additional materials and updates for this work will be available at http://clay- more.engineer.gvsu.edu/~jackh/books.html page ii 1.1 TODO LIST 1.4 2. PROGRAMMABLE LOGIC CONTROLLERS . . . . . . . . . . . . . 2.1 2.1 INTRODUCTION 2.1 2.1.1 Ladder Logic 2.1 2.1.2 Programming 2.6 2.1.3 PLC Connections 2.10 2.1.4 Ladder Logic Inputs 2.11 2.1.5 Ladder Logic Outputs 2.12 2.2 A CASE STUDY 2.13 2.3 SUMMARY 2.14 2.4 PRACTICE PROBLEMS 2.15 2.5 PRACTICE PROBLEM SOLUTIONS 2.15 2.6 ASSIGNMENT PROBLEMS 2.16 3. PLC HARDWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 3.1 INTRODUCTION 3.1 3.2 INPUTS AND OUTPUTS 3.2 3.2.1 Inputs 3.3 3.2.2 Output Modules 3.7 3.3 RELAYS 3.13 3.4 A CASE STUDY 3.14 3.5 ELECTRICAL WIRING DIAGRAMS 3.15 3.5.1 JIC Wiring Symbols 3.17 3.6 SUMMARY 3.21 3.7 PRACTICE PROBLEMS 3.21 3.8 PRACTICE PROBLEM SOLUTIONS 3.24 3.9 ASSIGNMENT PROBLEMS 3.27 4. LOGICAL SENSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 4.1 INTRODUCTION 4.1 4.2 SENSOR WIRING 4.1 4.2.1 Switches 4.2 4.2.2 Transistor Transistor Logic (TTL) 4.3 4.2.3 Sinking/Sourcing 4.3 4.2.4 Solid State Relays 4.10 4.3 PRESENCE DETECTION 4.11 4.3.1 Contact Switches 4.11 4.3.2 Reed Switches 4.11 4.3.3 Optical (Photoelectric) Sensors 4.12 4.3.4 Capacitive Sensors 4.19 4.3.5 Inductive Sensors 4.23 4.3.6 Ultrasonic 4.25 4.3.7 Hall Effect 4.25 page iii 4.3.8 Fluid Flow 4.26 4.4 SUMMARY 4.26 4.5 PRACTICE PROBLEMS 4.27 4.6 PRACTICE PROBLEM SOLUTIONS 4.30 4.7 ASSIGNMENT PROBLEMS 4.36 5. LOGICAL ACTUATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 5.1 INTRODUCTION 5.1 5.2 SOLENOIDS 5.1 5.3 VALVES 5.2 5.4 CYLINDERS 5.4 5.5 HYDRAULICS 5.6 5.6 PNEUMATICS 5.8 5.7 MOTORS 5.9 5.8 OTHERS 5.10 5.9 SUMMARY 5.10 5.10 PRACTICE PROBLEMS 5.10 5.11 PRACTICE PROBLEM SOLUTIONS 5.10 5.12 ASSIGNMENT PROBLEMS 5.11 6. BOOLEAN LOGIC DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 6.1 INTRODUCTION 6.1 6.2 BOOLEAN ALGEBRA 6.1 6.3 LOGIC DESIGN 6.6 6.3.1 Boolean Algebra Techniques 6.13 6.4 COMMON LOGIC FORMS 6.14 6.4.1 Complex Gate Forms 6.14 6.4.2 Multiplexers 6.15 6.5 SIMPLE DESIGN CASES 6.17 6.5.1 Basic Logic Functions 6.17 6.5.2 Car Safety System 6.18 6.5.3 Motor Forward/Reverse 6.18 6.5.4 A Burglar Alarm 6.19 6.6 SUMMARY 6.23 6.7 PRACTICE PROBLEMS 6.24 6.8 PRACTICE PROBLEM SOLUTIONS 6.27 6.9 ASSIGNMENT PROBLEMS 6.37 7. KARNAUGH MAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 7.1 INTRODUCTION 7.1 7.2 SUMMARY 7.4 7.3 PRACTICE PROBLEMS 7.4 7.4 PRACTICE PROBLEM SOLUTIONS 7.10 page iv 7.5 ASSIGNMENT PROBLEMS 7.16 8. PLC OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 8.1 INTRODUCTION 8.1 8.2 OPERATION SEQUENCE 8.3 8.2.1 The Input and Output Scans 8.4 8.2.2 The Logic Scan 8.4 page 0 A C + B C * B B T1 ST2 A⋅= T1 T2 T3 T4 ST1 ST2 ST3 FS = first scan ST1 ST1 T1+()T2⋅ FS+= ST2 ST2 T2 T3++()T1 T4⋅⋅= ST3 ST3 T4 T1⋅+()T3⋅= T2 ST1 B⋅= T3 ST3 CB⋅()⋅= T4 ST2 CB+()⋅= ST2 A ST1 B ST3 C B T1 T2 T3 T4 ST2 C B ST1 T2 ST1 T1 first scan ST2 T1 ST2 T2 T3 ST3 T3 ST3 T4 T4 T1 Automating Manufacturing Systems with PLCs (Version 4.2, April 3, 2003) Hugh Jack page i Copyright (c) 1993-2003 Hugh Jack (jackh@gvsu.edu). Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". This document is provided as-is with no warranty, implied or otherwise. There have been attempts to eliminate errors from this document, but there is no doubt that errors remain. As a result, the author does not assume any responsibility for errors and omissions, or damages resulting from the use of the information pro- vided. Additional materials and updates for this work will be available at http://clay- more.engineer.gvsu.edu/~jackh/books.html page ii 1.1 TODO LIST 1.4 2. PROGRAMMABLE LOGIC CONTROLLERS . . . . . . . . . . . . . 2.1 2.1 INTRODUCTION 2.1 2.1.1 Ladder Logic 2.1 2.1.2 Programming 2.6 2.1.3 PLC Connections 2.10 2.1.4 Ladder Logic Inputs 2.11 2.1.5 Ladder Logic Outputs 2.12 2.2 A CASE STUDY 2.13 2.3 SUMMARY 2.14 2.4 PRACTICE PROBLEMS 2.15 2.5 PRACTICE PROBLEM SOLUTIONS 2.15 2.6 ASSIGNMENT PROBLEMS 2.16 3. PLC HARDWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 3.1 INTRODUCTION 3.1 3.2 INPUTS AND OUTPUTS 3.2 3.2.1 Inputs 3.3 3.2.2 Output Modules 3.7 3.3 RELAYS 3.13 3.4 A CASE STUDY 3.14 3.5 ELECTRICAL WIRING DIAGRAMS 3.15 3.5.1 JIC Wiring Symbols 3.17 3.6 SUMMARY 3.21 3.7 PRACTICE PROBLEMS 3.21 3.8 PRACTICE PROBLEM SOLUTIONS 3.24 3.9 ASSIGNMENT PROBLEMS 3.27 4. LOGICAL SENSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 4.1 INTRODUCTION 4.1 4.2 SENSOR WIRING 4.1 4.2.1 Switches 4.2 4.2.2 Transistor Transistor Logic (TTL) 4.3 4.2.3 Sinking/Sourcing 4.3 4.2.4 Solid State Relays 4.10 4.3 PRESENCE DETECTION 4.11 4.3.1 Contact Switches 4.11 4.3.2 Reed Switches 4.11 4.3.3 Optical (Photoelectric) Sensors 4.12 4.3.4 Capacitive Sensors 4.19 4.3.5 Inductive Sensors 4.23 4.3.6 Ultrasonic 4.25 4.3.7 Hall Effect 4.25 page iii 4.3.8 Fluid Flow 4.26 4.4 SUMMARY 4.26 4.5 PRACTICE PROBLEMS 4.27 4.6 PRACTICE PROBLEM SOLUTIONS 4.30 4.7 ASSIGNMENT PROBLEMS 4.36 5. LOGICAL ACTUATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 5.1 INTRODUCTION 5.1 5.2 SOLENOIDS 5.1 5.3 VALVES 5.2 5.4 CYLINDERS 5.4 5.5 HYDRAULICS 5.6 5.6 PNEUMATICS 5.8 5.7 MOTORS 5.9 5.8 OTHERS 5.10 5.9 SUMMARY 5.10 5.10 PRACTICE PROBLEMS 5.10 5.11 PRACTICE PROBLEM SOLUTIONS 5.10 5.12 ASSIGNMENT PROBLEMS 5.11 6. BOOLEAN LOGIC DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 6.1 INTRODUCTION 6.1 6.2 BOOLEAN ALGEBRA 6.1 6.3 LOGIC DESIGN 6.6 6.3.1 Boolean Algebra Techniques 6.13 6.4 COMMON LOGIC FORMS 6.14 6.4.1 Complex Gate Forms 6.14 6.4.2 Multiplexers 6.15 6.5 SIMPLE DESIGN CASES 6.17 6.5.1 Basic Logic Functions 6.17 6.5.2 Car Safety System 6.18 6.5.3 Motor Forward/Reverse 6.18 6.5.4 A Burglar Alarm 6.19 6.6 SUMMARY 6.23 6.7 PRACTICE PROBLEMS 6.24 6.8 PRACTICE PROBLEM SOLUTIONS 6.27 6.9 ASSIGNMENT PROBLEMS 6.37 7. KARNAUGH MAPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 7.1 INTRODUCTION 7.1 7.2 SUMMARY 7.4 7.3 PRACTICE PROBLEMS 7.4 7.4 PRACTICE PROBLEM SOLUTIONS 7.10 page iv 7.5 ASSIGNMENT PROBLEMS 7.16 8. PLC OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 8.1 INTRODUCTION 8.1 8.2 OPERATION SEQUENCE 8.3 8.2.1 The Input and Output Scans 8.4 8.2.2 The Logic Scan 8.4 SIGNALS AND SYSTEMS [CHAP. 1 (a) x(r - 2) is sketched in Fig. 1-18(a). (6) x(20 is sketched in Fig. 1-18(b). (c) x(t/2) is sketched in Fig. 1-18(c). (d) X( -t) is sketched in Fig. 1-1Nd). (c) Fig. 1-18 1.2. A discrete-time signal x[n] is shown in Fig. 1-19. Sketch and label each of the following signals. (a) x[n - 21; (b) x[2n]; (c) x[-n]; (d) x[-n + 21 Fig. 1-19 CHAP. 11 SIGNALS AND SYSTEMS (a) x[n - 21 is sketched in Fig. 1-20(a). (b) x[2n] is sketched in Fig. 1-20(b). (c) x[-n] is sketched in Fig. 1-2Nc). (d) x[-n + 21 is sketched in Fig. 1-2Nd). (4 Fig. 1-20 13. Given the continuous-time signal specified by x(t) = (A - It' -1lfll otherwise determine the resultant discrete-time sequence obtained by uniform sampling of x(t) with a sampling interval of (a) 0.25 s, (b) 0.5 s, and (c) 1.0 s. It is easier to take the graphical approach for this problem. The signal x(t) is plotted in Fig. 1-21(a). Figures 1-21(b) to (dl give plots of the resultant sampled sequences obtained for the three specified sampling intervals. (a) T, = 0.25 s. From Fig. 1-21(b) we obtain x[n] = (. . . ,0,0.25,0.5,0.75,1,0.75,0.5,0.25,0,. . .) T (b) T, = 0.5 s. From Fig. 1-21(c) we obtain x[n]= { , 0,0.5,1,0.5,0 , I T SIGNALS AND SYSTEMS [CHAP. 1 (4 Fig. 1-21 (c) T, = 1 s. From Fig. 1-21(d) we obtain x[n] = (. . .,O, 1,O . .) = S[nl 1.4. Using the discrete-time signals x,[n] and x,[n] shown in Fig. 1-22, represent each of the following signals by a graph and by a sequence of numbers. (a) yJn1 =x,[nl +x,[nl; (b) y,[nI= 2x,[nl; (c) y,[nI =xJnIxJnl Fig. 1-22 CHAP. 11 SIGNALS AND SYSTEMS (a) y,[n] is sketched in Fig. 1-23(a). From Fig. 1-23(a) we obtain (b) y2[n] is sketched in Fig. 1-23(b). From Fig. 1-23(b) we obtain (c) yJn] is sketched in Fig. 1-23(c). From Fig. 1-23(c) we obtain (d Fig. 1-23 1.5. Sketch and label the even and odd components of the signals shown in Fig. 1-24. Using Eqs. (1.5) and (1.6), the even and odd components of the signals shown in Fig. 1-24 are sketched in Fig. 1-25. SIGNALS AND SYSTEMS [CHAP. 1 (4 Fig. 1-24 1.6. Find the even and odd components of x(r) = eJ'. Let x,(r) and x,(I) be the even and odd components of ei', respectively. eJ' =x,(I) +x,(I) From Eqs. (1.5) and (1.6) and using Euler's formula, we obtain x,( I) = $(eJr + e-J') = cos I x,,(I) = f(ei'-e-j') =jsint Show that the product of two even signals or of two odd signals is an even signal and that the product of an even and an odd signaI is an odd signal. Let x(t) =xl(t)x2(t). If XJI) and x2(l) are both even, then x(-l) =x,(-I)X,(-t) =xI(I)x2(t) =x(t) and x(t) is even. If x,(t) and x2(t) are both odd, then x(-I) =x,(-I)x,(-I) = -x,(t)[-x2(t)] =x1(t)x2(t) =x(t) and x(t) is even. If x,(t) is even and x2(f) is odd, then and X(I) is odd. Note that in the above proof, variable I represents either a continuous or a discrete variable. CHAP. 11 SIGNALS AND SYSTEMS (4 Fig. 1-25 SIGNALS AND SYSTEMS 1.8. Show that [CHAP. 1 (a) If x(t) and x[n] are even, then (b) If x(t) and x[n] are odd, then x(0) = 0 and x[O] =O k /a ~(r) dr = 0 and x x[n] =O -a n= -k (a) We can write Letting t = -A in the first integral on the right-hand side, we get Since x(t) is even, that is, x( -A) = x(A), we have Hence, Similarly, Letting n = -m in the first term on the right-hand side, we get Since x[n] is even, that is, x[ -m] =x[m], we have Hence, (1.75a) (I. 75b) (6) Since x(t) and x[n] are odd, that is, x( - t) = -x(t) and .. .Economic Systems Economics of Agricultural, Industrial, and Postindustrial Societies In an agricultural... population 8/22 Economic Systems Socialism The economies of China and Russia after World War II are examples of one form of socialism (Photo courtesy of Wikimedia Commons) Socialism is an economic system... Retrieved February 6, 2012 (http://siteresources.worldbank.org/INTDECINEQ/ Resources/fidrmuc .pdf) 20/22 Economic Systems Goldsborough, Reid 2010 "World's First Coin." 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