In Grapher, can functions be used to define parametric curves?

I'm drawing a curve using matrices in Grapher, for instance: However, any time I try to use a function (i.e. a(x)) as a matrix element: I get errors: I've looked through the unofficial manual, but it doesn't specifically say. If I'm not able to use a function as an element, I'd have to re-type the expression in multiple locations whenever I want to change it :(