chore: import upstream snapshot with attribution

2026-07-13 13:30:25 +08:00
commit f19b2512d7
562 changed files with 38082 additions and 0 deletions
@@ -0,0 +1,43 @@
+import numpy as np
+from prml.kernel.kernel import Kernel
+
+
+class PolynomialKernel(Kernel):
+    """
+    Polynomial kernel
+    k(x,y) = (x @ y + c)^M
+    """
+
+    def __init__(self, degree=2, const=0.):
+        """
+        construct Polynomial kernel
+
+        Parameters
+        ----------
+        const : float
+            a constant to be added
+        degree : int
+            degree of polynomial order
+        """
+        self.const = const
+        self.degree = degree
+
+    def __call__(self, x, y, pairwise=True):
+        """
+        calculate pairwise polynomial kernel
+
+        Parameters
+        ----------
+        x : (..., ndim) ndarray
+            input
+        y : (..., ndim) ndarray
+            another input with the same shape
+
+        Returns
+        -------
+        output : ndarray
+            polynomial kernel
+        """
+        if pairwise:
+            x, y = self._pairwise(x, y)
+        return (np.sum(x * y, axis=-1) + self.const) ** self.degree