Kernel Overloading Example

This example demonstrates kernel overloading using CodPy.

# import libraries
import numpy as np
from codpydll import *
import codpy.core as core


# define the class
class my_kernel(core.cd.kernel):
    # An example of overloading codpy kernel with a user-defined expression.

    def __init__(self, bandwith = 1.,**kwargs):
        core.cd.kernel.__init__(self)
        self.bandwidth_ = bandwith

    def k(self, x, y):
        out = np.linalg.norm((x - y) * self.bandwidth_)
        return out * out * 0.5

    def grad(self, x, y):
        return y * self.bandwidth_

Generate data for the kernel.

core.kernel_interface.set_verbose(True)
x, y = np.random.randn(3, 2), np.random.randn(3, 2)

Create a kernel object and display the result.

my_kernel1 = my_kernel(1)
my_kernel2 = my_kernel(2)
result_1 = my_kernel1.k(x[0], y[0])
print("Result 1:", result_1)

Result 1: 1.061301935547621

Set the kernel and display the next result. my_kernel2 and my_kernel_ptr2 are the same object.

my_kernel.set_kernel_ptr(my_kernel2)
my_kernel_ptr2 = core.kernel_interface.get_kernel_ptr()
result_2 = my_kernel_ptr2.k(x[0], y[0])
print("Result 2:", result_2)

Result 2: 4.245207742190484

Compute the Gram matrix with my_kernel2 and display it.

gram_matrix = core.op.Knm(x, y)
print("Gram Matrix:", gram_matrix)

Gram Matrix: [[ 4.24520774 12.6903989   0.26575161]
 [ 1.55932528 18.17264219  6.9421239 ]
 [ 5.10843915 16.41678959 11.85845957]]

You can switch kernel as follow.

my_kernel.set_kernel_ptr(my_kernel1)
print(core.op.Knm(x, y))
pass

[[1.06130194 3.17259972 0.0664379 ]
 [0.38983132 4.54316055 1.73553097]
 [1.27710979 4.1041974  2.96461489]]