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"valueAt" vs "value" functions

mikewu999

I need a Skill function that will return the value of a waveform at a specified time. There seem to be two choices: the Ocean function "value" and the ViVA function "valueAt". From the documentation the differences seem to be:

  • Interpolation: The Ocean manual explicitly says that "value" does interpolation and provides an option for interpolation type. The ViVA Skill manual doesn't mention interpolation for "valueAt". Does "valueAt" do interpolation?
  • Extrapolation: "valueAt" can optionally do extrapolation. What happens with "value" if I specify a timepoint past the end of the simulation?
  • Options: "value" has a lot more options and can return multiple values in a waveform as well as single values. "valueAt" seems to support only single return values.

What is the best practice regarding which function to use in the case where I only want the simple interpolated value Y at time X? Does it matter? Is one more computationally efficient or do they both call the same underlying function?

  • Some answers:

    • Yes, valueAt interpolates. It doesn't give the type of interpolation though (it's intended to be a simpler interface). The documentation should make this clear, I agree. Perhaps you can use the "feedback" buttons in the doc to request this is improved?
    • value extrapolates by default - in other words if you ask for a value at an x-axis value before the first or after the last point, it will return the first y or last y value. It has an optional argument to turn that off (which is available through the ViVA calculator form - it just isn't in the OCEAN reference manual for some reason).
    • Yes, this is true. valueAt is simpler, intentionally.

    If you want the simple behaviour you describe, it doesn't really matter, since valueAt is just calling value underneath anyway...

    Andrew

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