벡터 머신의 비선형 분류와 회귀를 가능하게 하는 수학적 기법인 커널 트릭에 대해 이야기했습
니다. 고차원 특성 공간에서의 선형 결정 경계는 원본 공간에서는 복잡한 비선형 결정 경계에 해
당한다는 것을 배웠습니다.
같은 기법을
PCA
에 적용해 복잡한 비선형 투영으로의 차원 축소를 가능하게 할 수 있습니다.
이를 커널
PCA
kernel
PCA
(
kPCA
)라고 합니다.
23
이 기법은 투영된 후에 샘플의 군집을 유지하
거나 꼬인 매니폴드에 가까운 데이터셋을 펼칠 때도 유용합니다.
예를 들어 다음 코드는 사이킷런의
KernelPCA
를 사용해
RBF
커널로
kPCA
를 적용하고 있습
니다(
RBF
커널과 다른 커널들에 대한 자세한 내용은
5
장을 참조하세요).
from sklearn
.
decomposition import KernelPCA
rbf
_
pca
=
KernelPCA
(
n
_
components
=
2
,
kernel
=
"
rbf
",
gamma
=
0
.
04
)
X
_
reduced ...
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