independentVarRef — References a predefined signal as an input to a function
varID- the internal XML identifier for the input signal
min(optional) - the allowable lower limit for the input signal
max(optional) - the allowable upper limit for the input signal
extrapolate(optional) - extrapolation flags for IV out-of-bounds (enumerated)
neither
min
max
both
interpolate(optional) - Interpolation flags for independent variable (enumerated)
discrete
floor
ceiling
linear
quadraticSpline
cubicSpline
An independentVarRef more fully describes the input mapping of the function by pointing to a separate breakpoint definition element. An optional extrapolate attribute describes how to extrapolate the output value when the input value exceeds specified values (default is 'neither,' meaning the value of the table is held constant at the nearest defined value). An optional interpolate attribute indicates how to perform the interpolation within the table (supporting discrete, linear, cubic or quadratic splines). There are three different discrete options: 'discrete' means nearest-neighbor, with an exact mid-point value being rounded in the positive direction; 'floor' means the function takes on the value associated with the next (numerically) higher independent breakpoint as soon as original value is exceeded, and 'ceiling' means the function holds the value associated with each breakpoint until the next (numerically) higher breakpoint value is reached by the independent argument. The default interpolation attribute value is 'linear.' This element allows reuse of common breakpoint values for many tables, but with possible differences in interpolation or extrapolation for each use.