Math Tips

本文深入探讨了组合数学中的加法法则、容斥原理、置换、排列与组合的概念及应用,通过具体例子如药物调配、扑克牌排列等问题,详细解析了如何运用这些原理解决实际问题,特别强调了重复组合问题的解决方法。

加法法则:

无重复元素A,B相加,得到AUB的元素数:|AUB|=|A|+|B|;

容斥原理就是考虑了重复元素的加法法则:|AUB|=|A|+|B|-|A^B|;

 

置换(substitution):将n个事物按顺序进行排列称为置换;不通置换总数为n!

排列(permutation):从n个事物取k个出来进行按顺序摆放称为排列;不同排列总数为P(n,k);

组合(combination):从n个事物取k个出来进行不按顺序摆放称为组合;不同组合总数为C(n,k);

C(n,k)=C(n-1,k-1)+C(n-1,k):解释,从n个事物取K个出来的总数等同于取出某个A的总数C(n-1,k-1)和不取出该A的总数C(n-1,k)的和

 

例子1:现有A、B、C三种药,混合后可调成一种药,新药调剂规则如下:从A、B、C三药总共取100颗,调剂时三种药品每种至少含有1颗,不考虑药品调剂顺序,同种药品每粒都相同。这种情况下,新药调剂的组合共有多少种?

tips:显然这是一个重复组合的问题,假设我们已经将100个空碟放为1列,每个盘可以装A,B,C中的其中一种药;我们可以用笔在这盘子的99个缝隙中画两笔,第1笔的左侧都放A,第2笔的右侧放C,两笔中间放B,则画笔摆放的组合就等同于药品调剂的组合的个数,于是一共有C(99,2)=99*98/2=4851

例子2:五张牌,2张王牌,J,Q,K各一张,排成一列,问左端或右端至少有一端是王牌的排法一共有多少种?

tips:总的排法减掉两端都不是王的排法:总排法=P(5,5)/2=60,两端都不是=p(3,2)*P(3,3)/2=18,一共42

 

一张普通的A4打印纸,没有人可以对折8次,为什么?

tips:一张A4纸张厚度为1mm,对折8次厚度为2^8=256mm=0.256m,你可以做到吗?

 

 

参考:《程序员的数学》 【日】结城浩 著

 

 

<think>Hmm, the user is asking for SageMath usage guidelines after providing three reference citations. Let me analyze this carefully. First, looking at the citations - they seem to be about specific SageMath implementations: [1] mentions an attack demonstration in cryptography context, [2] shows solving Lorentz system with ODEs, and [3] discusses performance considerations for field extensions. The user explicitly states these are just references though, not their actual need. The core request is clear: "I want to get SageMath usage methods" and directly asks for "SageMath usage guide". This appears to be a beginner seeking comprehensive learning resources rather than those specific technical examples. I recall in our history the user has shown interest in mathematical computing environments. Since they're asking about usage guides, they're probably new to SageMath or want systematic learning materials. The references they provided suggest they might be working on some mathematical computations already. For a good response, I should: 1. Focus on beginner-friendly learning paths rather than advanced examples 2. Provide structured resources from official channels 3. Include practical starting tips since installation is often the first hurdle 4. Suggest relevant mathematical modules as they mentioned "usage methods" 5. Offer next-step guidance through follow-up questions The user seems technically inclined given the references, so I can include both quick-start commands and conceptual explanations. The challenge is balancing depth with accessibility since I don't know their exact level. Perhaps organizing by: - Installation basics - Core interface options - Key mathematical features - Official documentation links - Community resources This structure should cover from absolute basics to self-guided learning. The examples in references suggest calculus/algebra applications, so I'll highlight those modules specifically. </think>以下是为您整理的SageMath使用指南,整合了关键功能和操作示例: ### 一、基础环境配置 1. **安装与启动** - 官方下载:https://www.sagemath.org/download.html - 云端版本:CoCalc(https://cocalc.com)支持在线使用 - 本地启动:终端执行 `sage` 进入交互环境 2. **环境设置** ```python # 加载自定义模块(引用[1]示例) load('main.sage') # 加载同目录下的SageMath文件 example_attack() # 执行文件中的函数 ``` ### 二、核心功能操作 #### 1. 符号计算 ```python var('x y') # 声明符号变量 eq = x^2 + y == 5 # 定义方程 solve(eq, x) # 解方程 → [x == -sqrt(-y + 5), x == sqrt(-y + 5)] ``` #### 2. 数值计算 ```python numerical_integral(sin(x), 0, pi) # 数值积分 → (1.9999999999999998, 2.220446049250313e-14) n(pi^2, digits=50) # 高精度计算 → 9.869604401089358 ``` #### 3. 微分方程求解(引用[2]示例) ```python var('x y z t') p, r, b = 10, 28, 3 # Lorenz系统参数 # 求解常微分方程组 RK4方法 solution = desolve_system_rk4([p*(y-x), x*(r-z)-y, x*y-b*z], [x,y,z], ics=[0,1,1,1], ivar=t, end_points=20, step=0.01) ``` ### 三、高级功能 #### 1. 抽象代数 ```python # 有限域扩展(引用[3]提示) F.<a> = GF(3^4, name='a') # 定义GF(3^4)域,显式命名提升性能 a^5 + a^2 + 1 # 域元素操作 ``` #### 2. 密码学应用(引用[1]关联) ```python # 椭圆曲线攻击示例(需预先实现算法) load('ec_attack.sage') castryck_decru_attack(Q, E) # 执行特定攻击 ``` ### 四、可视化工具 ```python # 绘制3D轨迹(Lorenz系统结果) line3d(solution[:,1:4], thickness=2, color='blue').show() ``` ### 五、性能优化建议 1. **预编译关键函数**: ```python cython(''' def fast_sum(long n): cdef long i, s=0 for i in range(n): s += i*i return s ''') ``` 2. **避免伪Conway多项式计算**(引用[3]提醒): - 显式声明有限域扩展名称可提速50%+ ### 六、学习资源 1. [官方教程](https://doc.sagemath.org/html/en/tutorial/) 2. [在线实验室](https://sagecell.sagemath.org) 3. 内置帮助系统: ```python search_doc("elliptic curve") # 文档检索 desolve? # 查看函数源码 ```
评论 1
成就一亿技术人!
拼手气红包6.0元
还能输入1000个字符
 
红包 添加红包
表情包 插入表情
 条评论被折叠 查看
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值