# Obtaining the equation type of an interpolated function

I used InterpolatingFunction on a set of points.

How can I know the type of that equation ? (polynomial, sinusoidal, logarithmic,etc...). I am looking for a general case answer.

Here is an example of dataset (among others, not necessarely of the same shape):

{-0.21970434400207, -0.22136596455224, -0.22074715867415, -0.21931620134959, -0.21774957192979, -0.21641976791018,-0.21554440918856, -0.21524028316217}

• Could you use FindFormula on the discrete data? – Chris K Jun 18 '19 at 15:06
• While FindFormula is indeed working for the simplest cases, it often breaks down for complicated functions. – Alex Jun 18 '19 at 15:28
• I imagine it's a tricky problem in general. Could you post some data sets that cause problems? – Chris K Jun 18 '19 at 15:32
• I just edited my question by giving an exemple. Hopefully this is a good one. For me the formula breaks down at the minima. – Alex Jun 18 '19 at 15:43
• If by "that equation" you mean the InterpolatingFunction, then the InterpolatingFunction does piecewise polynomial interpolation, cubic by default. See this Q&A, for instance. – Michael E2 Jun 18 '19 at 21:32