计算机科学选讲第五章.pptVIP

Computer Science: an overview Content The Concept of an Algorithm An Informal Review The Formal Definition of an Algorithm The Abstract Nature of Algorithm An Informal Review In our study, there are a multitude of algorithms converting numeric representations from one form to another, detecting and correcting errors in data, compressing and decompressing data files, controlling time-sharing in a multitasking environment, and many more. The machine cycle that is following by CPU is nothing more than the simple algorithm Algorithms are not restricted to technical activities The activity of shelling peas Every activity of the human mind is actually the result of algorithm execution Including imagination, creativity, and decision making The machine cycle The activity of shelling peas The set of steps in an algorithm are ordered The steps in an algorithm must have a well-established as structure in terms of the order in which its steps are executed The order here does not means that the step must be executed in a sequence consisting of a first step, followed by a second, and so on the Parallel algorithm contain more than one sequence of steps, each designed to be executed by different processors in a multiprocessor machine The algorithm’s structure may be that of multiple threads that branch and reconnect as different processors perform different parts of the overall task Next, an algorithm must consist of executable steps Make a list of all positive integers The executable is described by term effective, or doable Another, The step in an algorithm must be unambiguous During execution of an algorithm, the information in the state of the process must be sufficient to determine uniquely and completely the actions required by each step. The executing of each step in an algorithm does not require creative skills. Rather, it requires only the ability to follow directions An algorithm must define a terminating process The execution of an algorithm must lead to an