# 2D LUT (extrapolation) Simulink vs interp2

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Ilham Hardy on 15 Apr 2015
Hi,
I am trying to "converts" a Simulink model into a matlab script/function, but I stumbled upon the 2D Look Up table conversion.
The interp2 works fine if input values lies inside the table (interpolation). However when the one/more input values lie outside the look-up table, interp2 per default returns NaN. The NaN can be substituted by any scalar number. The 2D-LUT block needs to be converted is set to do linear extrapolation when the input values fall outside the table.
Is there any default function to do 2D-linear-extrapolation in Matlab? preferably with same working principle as in 2D-LUT block in Simulink?
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Ilham Hardy on 15 Apr 2015
Another angle:
Is there anyway to retrace the calculation done by 2D-lookup table in Simulink? Does 2D-LUT block calls specific Matlab function?

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### Answers (1)

Sebastian Castro on 15 Apr 2015
Looks like interp2 is designed to return NaNs by default unless your interpolation method is 'spline' .
You can change this by include the last 'scalar' argument after the interpolation method. For example,
Vq = interp2(V,Xq,Yq,'linear','scalar')
- Sebastian
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Sebastian Castro on 16 Apr 2015
Edited: Sebastian Castro on 16 Apr 2015
Whoops! Didn't notice that part -- that it's a single scalar value.
What about griddedInterpolant? That one definitely has various extrapolation methods.
There are two examples at the end of the above page for 2-D interpolation and 1-D extrapolation.
- Sebastian
Thushara De Silva on 9 Sep 2018
Is there an accepted answer for this question? I also have the same problem of extrapolating, however, I couldn't find the solution from those pages.

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