POJ 1045：Bode Plot

Bode Plot

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 13392		Accepted: 8462

Description

Consider the AC circuit below. We will assume that the circuit is in steady-state. Thus, the voltage at nodes 1 and 2 are given by v₁ = V_S coswt and v₂ = V_Rcos
(wt + q ) where V_S is the voltage of the source,w is the frequency (in radians per second),
and t is time. V_R is the magnitude of the voltage drop across the resistor, and q is its phase. 




You are to write a program to determine V_R for different values of w. You will need two laws of electricity to solve this problem. The first is Ohm's Law, which states v₂ = iR where
i is the current in the circuit, oriented clockwise. The second is i = C d/dt (v₁-v₂) which relates the current to the voltage on either side of the capacitor. "d/dt"indicates the derivative with respect to t. 

Input

The input will consist of one or more lines. The first line contains three real numbers and a non-negative integer. The real numbers are V_S, R, and C, in that order. The integer, n, is the number of test cases. The following n lines of the input
will have one real number per line. Each of these numbers is the angular frequency, w. 

Output

For each angular frequency in the input you are to output its corresponding V_R on a single line. Each V_R value output should be rounded to three digits after the decimal point.

Sample Input

1.0 1.0 1.0 9
0.01
0.031623
0.1
0.31623
1.0
3.1623
10.0
31.623
100.0

Sample Output

0.010
0.032
0.100
0.302
0.707
0.953
0.995
1.000
1.000

水题，公式推导。话说真不能再总纠结这水题了，越做越水了现在。

v₁ =
V_S

_{v2 =
VRcos (wt + q )} 

 _v2 =
iR

_{C=d/dt (v1-v2)
即(v1-v2)
对t求导}

_{已知Vs,C,R,w,求 VR。因为任意的t，等式都成立，所以对t取特殊值，解方程即可。}

代码：

#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;

int main()
{
	double Vs,R,C,w;
	int n,i;
	cin>>Vs>>R>>C>>n;

	for(i=1;i<=n;i++)
	{
		cin>>w;
		printf("%.3f",sqrt(1.0/(1+C*C*w*w*R*R))*C*w*R*Vs);
		cout<<endl;
	}
    return 0;
}

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