Term Block

A block that represents a local function whose value can be found and used as a term in a UserFunc expression (or in an <Expression>).

<Term>s are similar to Local UserFuncs; the difference is that <Term>s must take exactly the same arguments as the containing function, and they are treated like an <Input> in the containing function (although they shouldn’t appear in the inputOrder, and they are not arguments of the function).

Differences between Terms and local functions:

• A <Term> must take the exact same arguments as the UserFunc in which it appears.
• A <Term> is evaluated exactly once for every evaluation of its containing UserFunc; if, e.g., it appears multiple times in an expression, the same value will be used each time (even if the Term returns a random number). In contrast, a local function will be called anew when needed.
  • Often this distinction is moot; it becomes important when evaluation is contingent. For example, suppose a <Term f> and a local <UserFunc g> appear in expression = if(a, f, g()). The expression f is needed only if a evaluates to true, and g() must be evaluated only if a is false. In this case f will be evaluated regardless, while g() is evaluated only if a is false. Therefore, using a local function instead of a variable can sometimes save time.
  • Another difference involves non-deterministic functions, e.g., random-number generators. If f is a Term, and g() a local function, each of which returns a random number, then in expression = if(f < 0.5, f, 0.5) + if(g() < 0.5, g(), 0.5) the same value will be used for both appearances of f, but each appearance of g() will evaluate to a different number.

<UserFunc f>
  kind = expression
  inputOrder = [ y ]
  <Input y>
    kind = arbitraryVector
    types = [float]
  </Input>
  <Term mySqrVar>
    kind = expression
    inputOrder = [ y ] # same args as UserFunc f
    <Input y>
      kind = arbitraryVector
      types = [float]
    </Input>
    expression = y*y
  </Term>
  <Term myPlusOneSqrVar>
    kind = expression
    inputOrder = [ y ] # same args as UserFunc f
    <Input y>
      kind = arbitraryVector
      types = [float]
    </Input>
    expression = (y+1)*(y+1)
  </Term>
  expression = mySqrVar*myPlusOneSqrVar + y
</UserFunc>