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Annie
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How to set constraints of griddata results are all non-negative?

Asked by Annie
on 18 Aug 2019
Latest activity Answered by Walter Roberson
on 18 Aug 2019
I use the griddata function in matlab, but after the interpolation, the value of some points is less than 0. Is there any way to control the range of interpolation results?
That is to say, the results I want are all non-negative, but the results obtained after interpolation are somewhat less than 0.
Is there any way to set constraints?

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I use griddata to interpolate the existing data (61) (the interpolation result is 100), my data is percent, but the result of the interpolation is <0, there are also >100, how to control, so that the interpolation result is Between 0-100?

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2 Answers

Answer by Stephen Cobeldick on 18 Aug 2019
Edited by Stephen Cobeldick on 18 Aug 2019
 Accepted Answer

"Is there any way to control the range of interpolation results?"
You could simply adjust the output data yourself:
A = max(0,min(100,A))
Depending on your data values you might be able to change the input data values and/or the interpolation method, e.g. if you used a spline or similar, then you might be able to change for linear interpolation.

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Answer by Walter Roberson
on 18 Aug 2019

The griddata and interp1 and interp2 methods that do interpolation (so everything except nearest or next or prev) are all subject to "ringing" when there is a sharp transition 0 to 0 to positive, because none of them can handle sharp corners. The piecewise ones such as spline are best at such transitions, but do not always detect the transition at exactly the right boundaries.

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