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Basic_comphy_ch1

# Basic_comphy_ch1 -     1 Ch 1 Introduction References 1...

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Unformatted text preview:     1 Ch. 1 Introduction References: 1. J.H. Mathews, “ Numerical methods for computer science, engineering, and mathematics” , Ch. 1 2. T.M.R. Ellis et al., “ Fortran 90 programming” , Ch. 1     2 Outline 1.1 Why computation? 1.2 Computer 1.3 Binary number system 1.4 Integer data 1.5 Real data 1.6 Character data 1.7 Computer languages     3 1.1 Why computation? * Consider the following equation: x a  b  1 − x = Suppose a = 2 & b = -1/2:       2 x 2  x − 1 =  2 x − 1  x  1 = x = 1 / 2  or   − 1 => * In general, we don't have analytic solutions! We then need to consider numerical approximation. Example: a = 14 & b  =  0.0514 x 14 − 0.0514  1 − x = * This equation appears in the estimation of the mass fraction of the 4 He nuclei in a simplified core-collapse model of massive stars.     4 * In realistic situations, there are very few physical problems that can be solved analytically. * As physics students (or physicists), we need to have some knowledge of computer programming and numerical methods. * The followings are some astrophysical examples where computers can help us: 1. Simulation of the merger of two neutron stars NASA's Grand Challenge Project (http://www.wugrav.wustl.edu)     5 2. Simulation of Type II supernova explosion of a massive star (Janka et al. http://arxiv.org/abs/0706.3056)     6 3. Supernova 1987A: Formations of triple rings Numerical simulation by Morris & Podsiadlowski Science, 315, 1103 (2007)     7 1.2 Computer Internal memory Control unit Arithmetic logic unit Central processing unit (CPU) Main memory (RAM) Secondary memory (hard disk, CDs,...) Input devices (keyboard, scanner,....) Output devices (Screen, printer,...) Note: RAM = R andom- a ccess m emory     8 CU Orlon-Computational Grid Question: What computers do physicists use for their research? Answer: From PC to supercomputer, or even a cluster of supercomputers!     9 Data representation * Computer memories are composed of millions of switchs: ON or OFF * Each switch represents one binary digit ( bit ): ON state  1 OFF state  * A number of bits are group together to represent numbers in the binary number system . * A byte (B) = a group of 8 bits that are used together to represent a binary number. (eg: 10100110, 01110001,....) * Byte is the fundamental unit to measure the capacity of a computer's memory (eg: 1GB RAM, 100GB harddisk,...)     10 1.3 Binary number system Recall: For the usual base 10 number system, the number “ 1289” is expressed as: 1289 = 1 × 10 3  2 × 10 2  8 × 10 1  9 × 10 * In general, for a positive integer N : N = a m × 10 m  a m − 1 × 10 m − 1 ⋯ a 2 × 10 2  a 1 × 10 1  a × 10 where the digits a m are chosen from { 0,1,2,..,9 } * Decimal notation : N = a k a k − 1 ⋯ a 2 a 1 a 0  10 Subscript 10: base 10 system * If it is understood that 10 is the base: N = a k a k − 1 ⋯ a 2 a 1 a Example: we understand that 1289 = 1289...
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Basic_comphy_ch1 -     1 Ch 1 Introduction References 1...

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