what function could be a kernel what is the kernel function what function could be a kernel which is a kernel function what function could be a kernel what is a kernel function what function could be a kernel what function is known as kernel which function could be a kernel function what is a function that is a kernel what could be a kernel function what function is a kernel what function could be a kernel which function could be a kernel function? what is the definition of a kernel what is this kernel function what could be a kernel function what is the kernel function what is a kernel function what is the function of a kernel in machine learning