微积分I(标准路径) · 免费预览

§5.6 Numerical integration (continued)

当被积函数不存在初等代数原函数,因而无法使用微积分第一基本定理时,我们如何准确计算诸如 $\int_0^1 e^{-x^2} \, dx$ 这样的定积分?是否有一些方法可以在黎曼和中不使用极大的 $n$ 值的情况下得到精确的估计?

1. Overall observations regarding

Overall observations regarding

2. Summary

Summary

3. Endpoint sums depend only on endpoints

Three functions ff, gg, hh all satisfy value 22 at 00 and value 11 at 11. Their one panel sums L1L_1 and R1R_1 are

4. Simpson lands exactly on quadratics

For the test functions, S2=53S_2 = \frac{5}{3} for ff and S2=74S_2 = \frac{7}{4} for gg, matching the exact integrals 53\frac{5}{3} and 74\frac{7}{4}, while the third function's exact value 95\frac{9}{5} exceeds its S2=4324S_2 = \frac{43}{24}. The explanation is

5. Classifying a mystery function

For an unknown monotone, fixed concavity function on [3,6][3,6], we have L4=7.23>R4=6.75L_4 = 7.23 \gt R_4 = 6.75, with midpoint M4=7.05M_4 = 7.05 above trapezoid T4=6.99T_4 = 6.99. The function is

6. Why one integral resists everything

The integral ∫01xtan⁡(x) dx\int_0^1 x\tan(x)\,dx cannot be evaluated exactly with the chapter's tools because

7. Dam flow through sixty seconds

Flow rates 2000,2100,2400,3000,3900,5100,65002000, 2100, 2400, 3000, 3900, 5100, 6500 CFS are recorded every ten seconds. With M3=204000M_3 = 204000, T3=211000T_3 = 211000, and S6=6190003S_6 = \frac{619000}{3}, the best volume estimate is

8. Simpson value for the first test function

With M1=74M_1 = \frac{7}{4} and T1=32T_1 = \frac{3}{2} for the test function ff, compute Simpson's S2=2M1+T13S_2 = \frac{2M_1 + T_1}{3} as a fraction.

9. Best estimate for the mystery integral

For the unknown function with L4=7.23L_4 = 7.23, R4=6.75R_4 = 6.75, M4=7.05M_4 = 7.05, and T4=6.99T_4 = 6.99, Simpson's estimate S8=2M4+T43S_8 = \frac{2M_4 + T_4}{3} is the best available. Compute S8S_8, rounded to two decimals.

10. Midpoint value for the second test function

The test function gg satisfies g(12)=158g\left(\frac{1}{2}\right) = \frac{15}{8}. Compute the one panel midpoint estimate M1M_1 for ∫01g(x) dx\int_0^1 g(x)\,dx as a decimal.

11. Dam volume by midpoint

Using midpoint samples at t=10,30,50t = 10, 30, 50 seconds with panel width 2020, compute M3M_3 for the dam flow integral in cubic feet.

12. Exactness class of Simpson's rule

Simpson's rule integrates linear functions and quadratic functions exactly.

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