**Defined in theory: Unary-scalar-functions****Source code: unary-scalar-functions.lisp**

**Documentation:**The function value-at returns the value of a quantity at some point in 'time' (or whatever the independent state variable is). The 'time' argument is just a constant scalar-quantity, such as a time-quantity. If the quantity is a function-quantity, then its value-at is its function value applied to the 'time' argument. If the quantity is constant-quantity, then its value-at is the quantity itself for all 'times'.

**Arity:**3

(Nth-Domain Value-At 2 Scalar-Quantity) (Nth-Domain Value-At 1 Physical-Quantity) (=> (Value-At ?Q ?Time ?Val) (= ?Val (If (Function-Quantity ?Q) (Value ?Q ?Time) ?Q)))