Topic: Syntax for Sum, Product, Integrate

Had trouble with the syntax of Sum. Documentation is unclear to me. The issue probably relates to Product and Integrate functions as well. In custom functions, define f(x)=x. Then all these:
g(a,b)=Sum(f,a,b)       <-as per help file
g(a,b)=Sum(f(),a,b)
g(a,b)=Sum(f(x),a,b)

produce an error msg. It appears the syntax must be
g(x,a,b)=Sum(f(x),a,b)

with x required as a dummy variable in the function name. But this means Sum is not useful in a graph equation, since x will be determined by Sum, not the x axis. Instead, a graph equation would have to call the custom function as g(0,x), with the first argument being an unused placeholder. Do I understand this correctly? It would be nice to specify the increment variable (and step value?) and not require the placeholder. Intuitively, I expected
g(a,b)=Sum(f(x),x,a,b[,step])

which could be used anywhere. An optional step value, though not essential, can be convenient.

Re: Syntax for Sum, Product, Integrate

As you have found out the sum, product and integrate functions works a little strange. They  were implemented that way because it was easiest and good enough for what I needed. This however makes their usefulness rather limited.

Fortunately this has been improved in the beta version of Graph 4.4, where the functions now work as you would expect. You can now use $matches[1]. The step size is still not supported but I will consider adding it.