Consider the following statement from Deep Learning book (p. 327, chapter 9: Convolutional Networks)
In its most general form, convolution is an operation on two functions of a real-valued argument.
Suppose $f$ and $g$ are functions on which I want to apply convolution operation. What is meant by two functions of a "real-valued argument" in this context?
Does it mean $f$ and $g$ are real-valued functions? Or does it mean $f$ and $g$ are real functions? or any other?
Real-valued function: Function whose codomain is a subset of real numbers
Real function: Function whose domain and codomain are a subset of real numbers.