我想执行积分计算使用矩形和梯形方法使用多线程，以获得更快的结果。不幸的是，在我的例子中，执行多线程代码比执行标准顺序代码要慢。使用多线程比使用单线程慢得多-毕竟，它不应该是相反的吗？感觉线程越多，代码的执行速度就越慢。
此外，我注意到线程越多，积分结果的精度就越低。当使用梯形方法计算积分时，这一点尤其值得注意。
下面是我的代码：https://dotnetfiddle.net/jEPURO
代码语言：javascript运行复制using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
namespace ParallelProgramming.ConsoleApp
{
class Program
{
public static string IntegrationMethod { get; set; }
public static double IntervalBegin { get; set; }
public static double IntervalEnd { get; set; }
public static int NPrecisionValue { get; set; }
public static bool IsParallel { get; set; }
public static int ThreadValue { get; set; }
public static Stopwatch Stopwatch { get; set; }
public static double Result { get; set; }
static void Main(string[] args)
{
Console.WriteLine("Function | Elapsed Time | Estimated Integral");
Console.WriteLine("-----------------------------------------------------------------");
IntervalBegin = 5;
IntervalEnd = -2;
NPrecisionValue = 100000000;
//RectangularIntegration – Sequential
NumericalIntegrationMethods integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.RectangularIntegration(IntervalBegin, IntervalEnd, NPrecisionValue);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.RectangularIntegration)} – Sequential | {Stopwatch.Elapsed} | {Result}");
//RectangularIntegrationParallel - 1 thread
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.RectangularIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 1);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.RectangularIntegrationParallel)} – 1 Thread | {Stopwatch.Elapsed} | {Result}");
//RectangularIntegrationParallel - 2 threads
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.RectangularIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 2);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.RectangularIntegrationParallel)} – 2 Threads | {Stopwatch.Elapsed} | {Result}");
//RectangularIntegrationParallel - 3 threads
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.RectangularIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 3);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.RectangularIntegrationParallel)} – 3 Threads | {Stopwatch.Elapsed} | {Result}");
//RectangularIntegrationParallel - 4 threads
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.RectangularIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 4);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.RectangularIntegrationParallel)} – 4 Threads | {Stopwatch.Elapsed} | {Result}");
//TrapezoidalIntegration - Sequential
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.TrapezoidalIntegration(IntervalBegin, IntervalEnd, NPrecisionValue);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.TrapezoidalIntegration)} – Sequential | {Stopwatch.Elapsed} | {Result}");
//TrapezoidalIntegrationParallel – 1 Thread
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.TrapezoidalIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 1);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.TrapezoidalIntegrationParallel)} – 1 Thread | {Stopwatch.Elapsed} | {Result}");
//TrapezoidalIntegrationParallel – 2 Threads
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.TrapezoidalIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 2);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.TrapezoidalIntegrationParallel)} – 2 Threads | {Stopwatch.Elapsed} | {Result}");
//TrapezoidalIntegrationParallel – 3 Threads
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.TrapezoidalIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 3);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.TrapezoidalIntegrationParallel)} – 3 Threads | {Stopwatch.Elapsed} | {Result}");
//TrapezoidalIntegrationParallel – 4 Threads
integral = new();
Stopwatch = Stopwatch.StartNew();
Result = integral.TrapezoidalIntegrationParallel(IntervalBegin, IntervalEnd, NPrecisionValue, 4);
Stopwatch.Stop();
Console.WriteLine($"{nameof(integral.TrapezoidalIntegrationParallel)} – 4 Threads | {Stopwatch.Elapsed} | {Result}");
Console.WriteLine("Press any key to continue...");
Console.ReadLine();
}
}
public class NumericalIntegrationMethods
{
double Function(double x)
{
return x * x + 2 * x;
}
public double RectangularIntegration(double xp, double xk, int n)
{
double dx, integral = 0;
dx = (xk - xp) / n;
for (int i = 1; i <= n; i++)
{
integral += dx * Function(xp + i * dx);
//Console.WriteLine("Sekwencyjnie - iteracja {0} wątek ID: {1}", i, Thread.CurrentThread.ManagedThreadId);
}
return integral;
}
public double TrapezoidalIntegration(double xp, double xk, int n)
{
double dx, integral = 0;
dx = (xk - xp) / n;
for (int i = 1; i <= n; i++)
{
integral += Function(xp + i * dx);
//Console.WriteLine("Sekwencyjnie - iteracja {0} wątek ID: {1}", i, Thread.CurrentThread.ManagedThreadId);
}
integral += (Function(xp) + Function(xk)) / 2;
integral *= dx;
return integral;
}
public double RectangularIntegrationParallel(double xp, double xk, int n, int maxThreads)
{
double dx, integral = 0;
dx = (xk - xp) / n;
Parallel.For(1, n + 1, new ParallelOptions { MaxDegreeOfParallelism = maxThreads }, i =>
{
integral += dx * Function(xp + i * dx);
//Console.WriteLine("Równolegle - iteracja {0} wątek ID: {1}", i, Thread.CurrentThread.ManagedThreadId);
});
return integral;
}
public double TrapezoidalIntegrationParallel(double xp, double xk, int n, int maxThreads)
{
double dx, integral = 0;
dx = (xk - xp) / n;
Parallel.For(1, n + 1, new ParallelOptions { MaxDegreeOfParallelism = maxThreads }, i =>
{
integral += Function(xp + i * dx);
//Console.WriteLine("Równolegle - iteracja {0} wątek ID: {1}", i, Thread.CurrentThread.ManagedThreadId);
});
integral += (Function(xp) + Function(xk)) / 2;
integral *= dx;
return integral;
}
}
}下面是输出：
代码语言：javascript运行复制Function | Elapsed Time | Estimated Integral
-----------------------------------------------------------------
RectangularIntegration – Sequential | 00:00:00.9284260 | -65.33333210831276
RectangularIntegrationParallel – 1 Thread | 00:00:01.7040507 | -65.33333210831276
RectangularIntegrationParallel – 2 Threads | 00:00:01.7191484 | -65.33333210831276
RectangularIntegrationParallel – 3 Threads | 00:00:01.6888398 | -57.73164823448317
RectangularIntegrationParallel – 4 Threads | 00:00:01.5530828 | -65.33333210831276
TrapezoidalIntegration – Sequential | 00:00:00.7278303 | -65.33333333332568
TrapezoidalIntegrationParallel – 1 Thread | 00:00:01.4265208 | -65.33333333332568
TrapezoidalIntegrationParallel – 2 Threads | 00:00:02.3009881 | -33.110522448239216
TrapezoidalIntegrationParallel – 3 Threads | 00:00:01.6062253 | -57.02137898750542
TrapezoidalIntegrationParallel – 4 Threads | 00:00:01.9967140 | -18.120285251376426为什么会发生这种情况？我做错了什么？毕竟，使用的线程越多，结果应该越快。4个线程应该比3更快，3个线程应该比2更快，以此类推。如何使用更多的线程来获得更快的结果？