code: def _pca(x, k=2):
      "Compute PCA of `x` with `k` dimensions."
      x = x-torch.mean(x,0)
      U,S,V = torch.svd(x.t())
      return torch.mm(x,U[:,:k]f _pca(x, k=2):
      "Compute PCA of `x` with `k` dimensions."
      x = x-torch.mean(x,0)
      U,S,V = torch.svd(x.t())
      return torch.mm(x,U[:,:k])
docs: Compute PCA of `x` with `k` dimensions.