## S4 method for signature 'RadialKernel,matrix,matrix'
.kernel(object, x1, x2, ...)

## S4 method for signature 'RadialKernel'
print(x, ...)

## S4 method for signature 'RadialKernel'
show(object)

## S4 method for signature 'RadialKernel'
summary(object, ...)