An algorithm is a finite set of computational instructions, each instruction can be executed in finite time, to perform computation or problem solving by giving some value, or set of values as input to produce some value, or set of values as output. Algorithms are not dependent on a particular machine, programming language or compilers i.e. algorithms run in same manner everywhere. So the algorithm is a mathematical object where the algorithms are assumed to be run under machine with unlimited capacity.

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System modeling and computer simulation, recently has become one of the premier subject in the industry as well as Defence. It helps an engineer or a scientist to study a system with the help of mathematical models and computers. In other words, one can say, system simulation is nothing but an experiment with the help of computers, without performing actual experiment. It saves lot of money which is required, if we actually perform experiments with the real system. Present book, “System Modeling and Simulation” has been written by keeping engineering students as well as scientists especially defence scientists in mind. Earlier this manuscript was prepared only for the use of defence scientists which has now been extended to other engineering applications. Modeling of a weapon system is just an application of basic techniques of modeling and simulation, which are being discussed in chapter two and four. After my superannuation from Defence Research & Development Organisation, briefly called DRDO in 2000, when I joined the Punjab Technical University, and taught this subject to B. Tech and M. Tech students, the manuscript was rewritten, so that it should be useful to engineering students too. Although many of the examples have been taken from target damage, yet care has been taken to include other examples, from marketing, and mechanical engineering and other related subjects. My intentions are that this book should prove itself as a complete manual for system simulation and modeling. That is the reason, that basic subjects required for modeling and simulation, such as probability theory, numerical methods and C++ have also been included and discussed wherever required. Wherever possible, computer programmes have been given with the output.

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A system is a collection of components (subsystems) that work together to realize some objective. For example, the library system contains librarians, books, and periodicals as components to provide knowledge for its members. Every system has three activities or functions. These activities are input, processing and output. • Input: It involves capturing and assembling elements that enter the system to be processed. Inputs to the system are anything to be captured by the system from its environment. For example, raw materials. • Processing: It involves transformation processes that convert input to output. For example, a manufacturing process. • Output: It involves transferring elements that have been produced by a transformation process to their ultimate destinations. Outputs are the things produced by the system and sent into its environment. For example, finished products. The system also includes other two additional activities. These activities include feedback and control.

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Web technologies related to the interface between web servers and their clients. This information includes markup languages, programming interfaces and languages, and standards for document identification and display. In general web technology incorporates tools and techniques for web development. Web Development is a broad term for the work involved in developing a web site for World Wide Web. This can include web design, web content development, client liaison, client-side/server-side scripting, web server and network security configuration, and ecommerce development. However, among web professionals, "web development" usually refers to the main non-design aspects of building web sites: writing markup and coding. Web development can range from developing the simplest static single page of plain text to the most complex web-based internet applications, electronic businesses, or social network services. Web design is a broad term used to encompass the way that content (usually hypertext or hypermedia) is delivered to an end-user through the World Wide Web, using a web browser or other web-enabled software is displayed. The intent of web design is to create a website—a collection of online content including documents and applications that reside on a web servers. A website may include text, images, sounds and other content, and may be interactive.

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The word cryptography comes from two Greek words meaning “secret writing” and is the art and science of information hiding. This field is very much associated with mathematics and computer science with application in many fields like computer security, electronic commerce, telecommunication, etc. So cryptography is a subject that should be of interest to many people, especially because we now live in the Information Age, and our secrets can be transmitted in so many ways – email, cell phone, etc. – and all these channels need to be protected [ simon singh]. Secrecy and Encryption In the ancient days, cryptography was mostly referred to as encryption – the mechanism to convert the readable plaintext into unreadable (incomprehensible) text i.e. ciphertext, and decryption – the opposite process of encryption i.e. conversion of ciphertext back to the plaintext. Though the consideration of cryptography was on message confidentiality (encryption) in the past, nowadays cryptography considers the study and practices of authentication, digital signatures, integrity checking, and key management, etc. Encryption mostly provides the secrecy of massage being transmitted over the communication network. This is called confidentiality of massage. The only sender knows the keys and can decipher the massage.

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