作业:习题2.25、2.28(2).
Problem 1 (习题2.25).
设
\int{0}^{1} f(x) dx - Tn(f) = \int_{0}^{1} k(t) f'(t) dt,
k(t) = \frac{t{i-1} + ti}{2} - t, t \in [t{i-1}, ti], i = 1, 2, \dots, n,
是复化梯形和,ti(i=0,1,…,n) 为积分区间[0,1] 的等分节点,记h=ti−ti−1=n1。
解.
在区间[ti−1,ti] 上,若∈[ti−1,ti],则有
记子区间上的误差为:
我们将f(x) 用积分表示代入:
利用f(ti)=f(ti−1)+∫ti−1tif′(t)dt,代入得:
交换积分次序:
代入得:
由于h=ti−ti−1,有2ti−1+ti=ti−2h,因此:
于是:
故总误差为:
综上:
∎
Problem 2 (习题2.28(2)).
利用自适应Simpson方法计算下列积分(精确至10−6):
Remark 1.
CodeBlock Loading...
- h:=b−a,S1:=6h[f(a)+4f(2a+b)+f(b)]
- S:=∑k=0n−1[2f(a+(k+41)h)−f(a+(k+21)h)+2f(a+(k+43)h)]
CodeBlock Loading...
判断∣S2−S1∣<ϵ?若是,则转步骤5
- h:=h/2,S1:=S2,
转步骤2
输出S2
解.
这个计算量有点大,我才用计算机来计算每一步的求解过程:
CodeBlock Loading...
\caption{求解最终结果}
|
迭代次数 |h |n |S1 |S2 |∣S2−S1∣ | 是否继续? |
| --- | --- | --- | --- | --- | --- | --- |
|
初始 | 8.0000 | 1 | 5.4901960784 | -- | -- | -- |
| 1 | 8.0000 | 1 | 5.4901960784 | 2.4784313725 | 3.0117647059 | 继续 |
| 2 | 4.0000 | 2 | 2.4784313725 | 2.5725490196 | 0.0941176471 | 继续 |
| 3 | 2.0000 | 4 | 2.5725490196 | 2.6477345635 | 0.0751855439 | 继续 |
| 4 | 1.0000 | 8 | 2.6477345635 | 2.6516272830 | 0.0038927194 | 继续 |
| 5 | 0.5000 | 16 | 2.6516272830 | 2.6516352807 | 0.0000079977 | 继续 |
| 6 | 0.2500 | 32 | 2.6516352807 | 2.6516353244 | 0.0000000438 |∣S2−S1∣<10−6,终止! |
| |
我们在第6次迭代后得到结果为:S2=2.6516353244,即:
Remark 2.
CodeBlock Loading...
∎
\caption{第1次迭代详细计算}
|
子区间 |x1 |x2 |x3 | 项值 |
| --- | --- | --- | --- | --- |
|
0 |x1=−2.0000 |x2=0.0000 |x3=2.0000 |−0.200000 |
| |f=0.200000 |f=1.000000 |f=0.200000 | |
| |
[1em]
S=−0.2000000000
S2=0.5×5.4901960784+68×(−0.2000000000)=2.4784313725\caption{第2次迭代详细计算}
|
子区间 |x1 |x2 |x3 | 项值 |
| --- | --- | --- | --- | --- |
|
0 |x1=−3.0000 |x2=−2.0000 |x3=−1.0000 |1.000000 |
| |f=0.100000 |f=0.200000 |f=0.500000 | |
| 1 |x1=1.0000 |x2=2.0000 |x3=3.0000 |1.000000 |
| |f=0.500000 |f=0.200000 |f=0.100000 | |
| |
[1em]
S=2.0000000000
S2=0.5×2.4784313725+64.0×2.0000000000=2.5725490196\caption{第3次迭代详细计算}
|
子区间 |x1 |x2 |x3 | 项值 |
| --- | --- | --- | --- | --- |
|
0 |x1=−3.5000 |x2=−3.0000 |x3=−2.5000 |0.326805 |
| |f=0.075472 |f=0.100000 |f=0.137931 | |
| 1 |x1=−1.5000 |x2=−1.0000 |x3=−0.5000 |1.715385 |
| |f=0.307692 |f=0.500000 |f=0.800000 | |
| 2 |x1=0.5000 |x2=1.0000 |x3=1.5000 |1.715385 |
| |f=0.800000 |f=0.500000 |f=0.307692 | |
| 3 |x1=2.5000 |x2=3.0000 |x3=3.5000 |0.326805 |
| |f=0.137931 |f=0.100000 |f=0.075472 | |
| |
[1em]
S=4.0843801612
S2=0.5×2.5725490196+62.0×4.0843801612=2.6477345635\caption{第4次迭代项值汇总(n=8)}
|
子区间 | 项值 |
| --- | --- |
|
0 ([-4.00, -3.00]) | 0.230281 |
| 1 ([-3.00, -2.00]) | 0.425543 |
| 2 ([-2.00, -1.00]) | 0.965103 |
| 3 ([-1.00, 0.00]) | 2.362353 |
| 4 ([0.00, 1.00]) | 2.362353 |
| 5 ([1.00, 2.00]) | 0.965103 |
| 6 ([2.00, 3.00]) | 0.425543 |
| 7 ([3.00, 4.00]) | 0.230281 |
| |
[1em]
S=7.9665600072
S2=0.5×2.6477345635+61.0×7.9665600072=2.6516272830\caption{第5次迭代项值汇总(n=16)}
|
子区间 | 项值 |
| --- | --- |
|
0 ([-4.00, -3.50]) | 0.199924 |
| 1 ([-3.50, -3.00]) | 0.260702 |
| 2 ([-3.00, -2.50]) | 0.352529 |
| 3 ([-2.50, -2.00]) | 0.498834 |
| 4 ([-2.00, -1.50]) | 0.746109 |
| 5 ([-1.50, -1.00]) | 1.184407 |
| 6 ([-1.00, -0.50]) | 1.930946 |
| 7 ([-0.50, 0.00]) | 2.781479 |
| 8 ([0.00, 0.50]) | 2.781479 |
| 9 ([0.50, 1.00]) | 1.930946 |
| 10 ([1.00, 1.50]) | 1.184407 |
| 11 ([1.50, 2.00]) | 0.746109 |
| 12 ([2.00, 2.50]) | 0.498834 |
| 13 ([2.50, 3.00]) | 0.352529 |
| 14 ([3.00, 3.50]) | 0.260702 |
| 15 ([3.50, 4.00]) | 0.199924 |
| |
[1em]
S=15.9098596702S2=0.5×2.6516272830+60.5×15.9098596702=2.6516352807
\caption{第6次迭代项值汇总(n=32)}
|
子区间范围 | 项值 | 子区间范围 | 项值 |
| --- | --- | --- | --- |
|
([-4.00, -3.75]) | 0.187485 | ([0.00, 0.25]) | 2.939678 |
| ([-3.75, -3.50]) | 0.212367 | ([0.25, 0.50]) | 2.624040 |
| ([-3.50, -3.25]) | 0.242391 | ([0.50, 0.75]) | 2.158277 |
| ([-3.25, -3.00]) | 0.279019 | ([0.75, 1.00]) | 1.702783 |
| ([-3.00, -2.75]) | 0.324245 | ([1.00, 1.25]) | 1.327892 |
| ([-2.75, -2.50]) | 0.380824 | ([1.25, 1.50]) | 1.040860 |
| ([-2.50, -2.25]) | 0.452615 | ([1.50, 1.75]) | 0.826277 |
| ([-2.25, -2.00]) | 0.545078 | ([1.75, 2.00]) | 0.665981 |
| ([-2.00, -1.75]) | 0.665981 | ([2.00, 2.25]) | 0.545078 |
| ([-1.75, -1.50]) | 0.826277 | ([2.25, 2.50]) | 0.452615 |
| ([-1.50, -1.25]) | 1.040860 | ([2.50, 2.75]) | 0.380824 |
| ([-1.25, -1.00]) | 1.327892 | ([2.75, 3.00]) | 0.324245 |
| ([-1.00, -0.75]) | 1.702783 | ([3.00, 3.25]) | 0.279019 |
| ([-0.75, -0.50]) | 2.158277 | ([3.25, 3.50]) | 0.242391 |
| ([-0.50, -0.25]) | 2.624040 | ([3.50, 3.75]) | 0.212367 |
| ([-0.25, 0.00]) | 2.939678 | ([3.75, 4.00]) | 0.187485 |
| |
[1em]
S=31.8196244180S2=0.5×2.6516352807+60.25×31.8196244180=2.6516353244
PDF
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