I have read the wiki page (https://en.wikipedia.org/wiki/Functional_(mathematics) but it is not helping.
I understand what a regular function is
input > do something to that input > output.
but not what functional is,
Wikipedia says "from a vector space into its underlying field of scalars"
That wording is confusing.
So the input is a vector but the output is a scalar? The only way I know to get scalar from vector is a dot product.
And a vector is just written as , if you take that as an input isn't it just essentially a regular function of 2 variables? y=f(a,b)