问题描述
我正在查看性能基准：
I was looking over the performance benchmarks: http://eigen.tuxfamily.org/index.php?title=Benchmark
我不禁注意到本征似乎始终优于所有专门的供应商库。问题是：怎么可能？有人会假定mkl / goto将使用处理器特定的调整代码，而本征则相当通用。
I could not help but notice that eigen appears to consistently outperform all the specialized vendor libraries. The questions is: how is it possible? One would assume that mkl/goto would use processor specific tuned code, while eigen is rather generic.
请注意，本质上是一个dgemm。对于N = 1000，本征大约为17Gf，而MKL仅12Gf
Notice this http://download.tuxfamily.org/eigen/btl-results-110323/aat.pdf, essentially a dgemm. For N=1000 Eigen gets roughly 17Gf, MKL only 12Gf
推荐答案
本征的评估很懒。来自：
Eigen has lazy evaluation. From How does Eigen compare to BLAS/LAPACK?:
是 Y = a * X + b * Y ，这是Eigen专门设计的。毫无疑问，图书馆在创建基准时胜出。您会注意到，更通用的基准测试（例如矩阵-矩阵乘法）对Eigen没有任何优势。
The second chart in the benchmarks is Y = a*X + b*Y, which Eigen was specially designed to handle. It should be no wonder that a library wins at a benchmark it was created for. You'll notice that the more generic benchmarks, like matrix-matrix multiplication, don't show any advantage for Eigen.
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