Interp - Strange Cubic Shape

Hi All,

I'm posting as I am trying to figure out if my expectations are wrong (probably), or if the Interp function is doing something strange.

In the following flow Series are simply numbers from 0 to 1 in steps of .05

This is the result, which I really don't understand. A simple interpolation between three points should yield a very simple, smooth curve, no?

If I replace the inputs with 0.5, 0.8, 0.5 I get something much nicer as follows:

Anyone have any idea why Interp is giving me such a complex curve in the first instance, and such a clean curve in the second?

Cheers,

Tom.

Replies to This Discussion

Permalink Reply by Vongsawat Wongkijjalerd on July 8, 2016 at 12:34pm

to expand on Marcus' reply: right-click Interpolate Data, change from Cubic to Linear

Permalink Reply by Tom D. on July 8, 2016 at 12:40pm

No - it is not linear, it is cubic, purposely so.

If I select linear I just get two straight segments, which is not what I want. I want a nice smooth curve.

Basically I was assuming I would get the curve in the screenshot below, which goes thru my three points. I can't understand why Interp is giving me such a complicated set of points.

Permalink Reply by Tom D. on July 8, 2016 at 1:19pm

Hi Marcus -

I was originally thinking of doing that although ultimately I am after numbers, not a curve. It feels like a bit heavy to start with numbers, produce 3D curve, evaluate that curve at difference positions to get my numbers which then get used in my flow. Since there is an Interp function for data I thought I would use that, but was surprised to see what it produced... I may end up going back to the approach you suggest, however, since that will give me more control on the shape of the curve. Thanks for the input!

Tom

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