当我尝试分析慢速优化算法时，我发现以下方法花费的时间比预期的要长得多：
protected virtual bool Dominates(ILInArray<double> p1, ILInArray<double> p2, int nObjectives)
{
using (ILScope.Enter(p1, p2))
{
ILArray<double> p1In = p1;
ILArray<double> p2In = p2;
bool strong = false;
for (int i = 0; i < nObjectives; i++)
{
using (ILScope.Enter())
{
if (p1In[i] > p2In[i])
strong = true;
else if (p1In[i] < p2In[i])
{
return false;
}
}
}
return strong;
}
}
然后我用以下实现替换它，并且速度增加了一个巨大的倍数。
protected virtual bool DominatesSys(double[] p1, double[] p2, int nObjectives)
{
bool strong = false;
for (int i = 0; i < nObjectives; i++)
{
if (p1[i] > p2[i])
strong = true;
else if (p1[i] < p2[i])
{
return false;
}
}
return strong;
}
我不理解它，并试图写一个测试来比较差异。以下是使用的测试代码：
[Test]
public void TestILNumericsSpeed()
{
ILArray<double> p1Il = ILMath.rand(100);
ILArray<double> p2Il = p1Il - 0.01;
double[] p1 = p1Il.GetArrayForRead();
double[] p2 = p2Il.GetArrayForRead();
int length = p1.Length;
Func<bool> func1 = () =>
{
Dominates(p1Il, p2Il, length);
return true;
};
Func<bool> func2 = () =>
{
DominatesSys(p1, p2, length);
return true;
};
var stats1 = CollectStats(func1, 20, 1000);
var stats2 = CollectStats(func2, 20, 1000);
log.InfoFormat("Mean time taken by ILNumerics = {0}.", stats1.Skip(1).Average(t => t.TotalSeconds));
log.InfoFormat("Mean time taken by system array = {0}.", stats2.Skip(1).Average(t => t.TotalSeconds));
}
protected virtual IList<TimeSpan> CollectStats(Func<bool> func, int n = 100, int nPerRound = 100)
{
Stopwatch watch = new Stopwatch();
var stats1 = new List<TimeSpan>();
watch.Reset();
for (int i = 0; i < n; i++)
{
using (ILScope.Enter())
{
watch.Reset();
watch.Start();
for (int j = 0; j < nPerRound; j++)
{
bool ret = func();
Assert.IsTrue(ret);
}
watch.Stop();
stats1.Add(watch.Elapsed);
}
}
return stats1;
}
我对获得的奇怪结果感到非常震惊。我期望ILArray在顺序索引方面比系统数组慢一点，但是1000次太多了。有人可以帮助诊断我的问题：
[INFO ] | 14:38:19,974 | [odes] | NumericsTest 383 | Mean time taken by ILNumerics = 0.294103963157895.
[INFO ] | 14:38:20,036 | [odes] | NumericsTest 383 | Mean time taken by system array = 0.000271984210526316.
根据Haymo的建议，运行以下测试来比较不同实现的速度。我认为在这种情况下，由于不需要使用DominatesSys创建中间数组，因此其性能最快。
[Test]
public void TestILNumericsSpeed()
{
ILArray<double> p1Il = ILMath.rand(1000);
ILArray<double> p2Il = p1Il - 0.01;
double[] p1 = p1Il.GetArrayForRead();
double[] p2 = p2Il.GetArrayForRead();
int length = p1Il.S[0];
Func<bool> func1 = () =>
{
Dominates1(p1Il, p2Il, length);
return true;
};
Func<bool> func2 = () =>
{
Dominates2(p1Il, p2Il, length);
return true;
};
Func<bool> func3 = () =>
{
Dominates3(p1Il, p2Il, length);
return true;
};
Func<bool> func4 = () =>
{
Dominates4(p1Il, p2Il, length);
return true;
};
Func<bool> func5 = () =>
{
Dominates5(p1Il, p2Il, length);
return true;
};
Func<bool> funcSys = () =>
{
DominatesSys(p1, p2, length);
return true;
};
var stats1 = IO.CollectStats(func1, 10, 1000);
var stats2 = IO.CollectStats(func2, 10, 1000);
var stats3 = IO.CollectStats(func3, 10, 1000);
var stats4 = IO.CollectStats(func4, 10, 1000);
var stats5 = IO.CollectStats(func5, 10, 1000);
var statsSys = IO.CollectStats(funcSys, 10, 1000);
log.InfoFormat("Mean time taken by Dominates1 = {0}.", stats1.Skip(1).Average(t => t.TotalSeconds));
log.InfoFormat("Mean time taken by Dominates2 = {0}.", stats2.Skip(1).Average(t => t.TotalSeconds));
log.InfoFormat("Mean time taken by Dominates3 = {0}.", stats3.Skip(1).Average(t => t.TotalSeconds));
log.InfoFormat("Mean time taken by Dominates4 = {0}.", stats4.Skip(1).Average(t => t.TotalSeconds));
log.InfoFormat("Mean time taken by Dominates5 = {0}.", stats5.Skip(1).Average(t => t.TotalSeconds));
log.InfoFormat("Mean time taken by system array = {0}.", statsSys.Skip(1).Average(t => t.TotalSeconds));
}
protected virtual bool Dominates1(ILInArray<double> p1, ILInArray<double> p2, int nObjectives)
{
using (ILScope.Enter(p1, p2))
{
ILArray<double> p1In = p1;
ILArray<double> p2In = p2;
bool strong = false;
for (int i = 0; i < nObjectives; i++)
{
using (ILScope.Enter())
{
if (p1In[i] > p2In[i])
strong = true;
else if (p1In[i] < p2In[i])
{
return false;
}
}
}
return strong;
}
}
protected virtual bool Dominates2(ILInArray<double> p1, ILInArray<double> p2, int nObjectives)
{
using (ILScope.Enter(p1, p2))
{
ILArray<double> n = p1[r(0, nObjectives - 1)] - p2[r(0, nObjectives - 1)];
if (any(n < 0)) return false;
return any(n > 0);
}
}
protected virtual bool Dominates3(ILInArray<double> p1, ILInArray<double> p2, int nObjectives)
{
using (ILScope.Enter(p1, p2))
{
ILArray<double> n = p1[r(0, nObjectives - 1)] - p2[r(0, nObjectives - 1)];
var strong = false;
foreach (var d in n)
{
if (d < 0) return false;
if (d > 0) strong = true;
}
return strong;
}
}
protected virtual bool Dominates4(ILInArray<double> p1, ILInArray<double> p2, int nObjectives)
{
using (ILScope.Enter(p1, p2))
{
ILArray<double> p1In = p1;
ILArray<double> p2In = p2;
bool strong = false;
for (int i = 0; i < nObjectives; i++)
{
using (ILScope.Enter()) { // probably does not help with such tiny arrays ...
if (p1In.GetValue(i) > p2In.GetValue(i))
strong = true;
else if (p1In.GetValue(i) < p2In.GetValue(i))
{
return false;
}
}
}
return strong;
}
}
protected virtual bool Dominates5(ILArray<double> p1, ILArray<double> p2, int nObjectives)
{
bool strong = false;
for (int i = 0; i < nObjectives; i++)
{
if (p1.GetValue(i) > p2.GetValue(i))
strong = true;
else if (p1.GetValue(i) < p2.GetValue(i))
return false;
}
return strong;
}
protected virtual bool DominatesSys(double[] p1, double[] p2, int nObjectives)
{
bool strong = false;
for (int i = 0; i < nObjectives; i++)
{
if (p1[i] > p2[i])
strong = true;
else if (p1[i] < p2[i])
{
return false;
}
}
return strong;
}
结果如下：
[INFO ] | 12:55:01,911 | [odes] | NumericsTest 379 | Mean time taken by Dominates1 = 2.85064264444444.
[INFO ] | 12:55:01,976 | [odes] | NumericsTest 380 | Mean time taken by Dominates2 = 0.0402656666666667.
[INFO ] | 12:55:01,977 | [odes] | NumericsTest 381 | Mean time taken by Dominates3 = 0.173880833333333.
[INFO ] | 12:55:01,978 | [odes] | NumericsTest 382 | Mean time taken by Dominates4 = 0.148000711111111.
[INFO ] | 12:55:01,979 | [odes] | NumericsTest 383 | Mean time taken by Dominates5 = 0.0593142444444444.
[INFO ] | 12:55:01,980 | [odes] | NumericsTest 383 | Mean time taken by system array = 0.00180445555555556.
答案 0 :(得分：1)
你的时间太小了。可能你的问题也是如此。增加两者（迭代次数，问题大小）以获得更可靠的结果。另外，不要忘记从测量中排除第一次迭代（由于JIT编译的开销要大得多）。
我怀疑，1000的因素是可靠的。但总的来说很明显，以你的方式迭代ILArray不能带来与迭代double []相同的性能。 ILNumerics的工作方式（你应该适应）是矢量化。以整个数组涉及计算而不是单个元素的方式重写算法。
如果无法做到这一点，那么为这样的微内核打破ILArray是没有错的。您使用的方式（GetArrayForRead（），GetArrayForWrite（））就可以了，以便访问底层系统数组并将其用于此类元素计算。
您可以尝试的另一种方法如下：
protected virtual bool Dominates(ILInArray<double> p1, ILInArray<double> p2, int nObjectives) {
using (ILScope.Enter(p1, p2)) {
ILArray<double> p1In = p1;
ILArray<double> p2In = p2;
bool strong = false;
for (int i = 0; i < nObjectives; i++) {
//using (ILScope.Enter()) { // probably does not help with such tiny arrays ...
if (p1In.GetValue(i) > p2In.GetValue(i))
strong = true;
else if (p1In.GetValue(i) < p2In.GetValue(i)) {
return false;
}
//}
}
return strong;
}
}
但更有希望的是，IMO会是这样的:(期望在从ILMath派生的类的上下文中的代码，因此ILMath。被忽略）
protected virtual bool Dominates(ILInArray<double> p1, ILInArray<double> p2, int nObjectives) {
using (ILScope.Enter(p1, p2)) {
ILArray<double> n = p1 - p2;
if (any(n < 0)) return false;
return any(n > 0);
}
}
请再次测量并告诉我们您的结果！感谢
@Edit：再想一想，还有另外一个选择：
protected virtual bool Dominates(ILInArray<double> p1, ILInArray<double> p2, int nObjectives) {
using (ILScope.Enter(p1, p2)) {
ILArray<double> n = p1 - p2;
var strong = false;
foreach (var d in n) {
if (d < 0) return false;
if (d > 0) strong = true;
}
return strong;
}
}
如果p1.Length != p2.Length，您可以相应地调整p1 - p2 ...