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期中复习过一遍ppt,理解大多数知识点(像割线法也要理解),然后做一套19年原题就行了。 | ||
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# 2022期中回忆版 | ||
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记得不全,可以用来提示复习内容 | ||
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## 选择填空题: | ||
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- 和19年第1题差不多 | ||
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- 哪些方法可以改变问题的病态性 | ||
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> 选项有高精度 等,当然高精度不是正确答案 | ||
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- 哪些误差不是某方法里面存在的 | ||
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> 考察对各种误差的理解,包括模型误差、舍入误差等 | ||
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- 手算一个割线法 | ||
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- 定理1.2 定理1.3那个,误差和前p位有效数字 之间的关系 | ||
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- CSR相比COO可以节省百分之多少的空间 (C. 25% D.10%) | ||
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> 个人理解这个节省比例应该是一个范围内,至多达到25% | ||
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- Ax=b,给出A,以下矩阵都是A矩阵的变换(行变换得到的新矩阵),问哪个矩阵可以使得G-S迭代法收敛 | ||
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> 结果是要考虑对角占优矩阵的G-S迭代法收敛。注意复习三种迭代法的收敛条件。 | ||
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- 泰勒展开里面 | ||
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$$ | ||
e^{-x} = 1 - x + {x^2 \over 2!} - {x^3 \over 3!} + \dots | ||
$$ | ||
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计算机用上式算$e^{-x}$,x取30会有什么问题? 计算$e^{-30}$的一个比较好的方法是什么? | ||
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- 给一个矩阵,若其减去$\lambda I$后不能LU分解,$\lambda$的取值至多可以有多少个 | ||
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> (只需要使得前n-1个顺序主子式有一个是0即可,对第i个顺序主子式,$\lambda$至多可以取i种值,所以就是1+2+...+n-1) | ||
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## 大题: | ||
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- 19年原题,第五题 $F=a^2-b^2$考虑浮点数误差那个 | ||
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- 牛顿法解线性方程组,和19年第三题差不多,改了数据。迭代一步,算一个部分主元LU分解,然后$PA=LU$,计算$A^{-1}b$时需要倒着乘$U^{-1}L^{-1}Pb$ | ||
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- cholesky分解,19年的原题(第四题) | ||
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- JOR迭代法,就是SOR迭代法里面,对x的每一维取值$x_i$,都单独设置一个$w_i$,然后用式子表示JOR迭代方程,并证明他是分裂法。 | ||
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> 设一个向量$\Omega = [\omega_1, ...,\omega_n]^T$,然后在SOR迭代法中将$\omega$换成$\Omega$即可 | ||
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