# Extrapolation 2-D lookup table

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jose tapia on 26 Mar 2011
Commented: hang x on 28 Jul 2020
Hi, I'm having the following problem. I have a 2d table that contains data from some measurements. How can I do the same kind of Extrapolation that is possible in SIMULINK 2-D table lookup using interpolation-extrapolation lookup method, but in Matlab. As I figured out 'griddata' and 'interp2' can not do the job for me. This is the dimension of my data:
x [1x37]
y [1x28]
z [28x37]
Titus Edelhofer on 22 Nov 2011
Hi Jette, nice to meet you again ;-). Titus

Matt Fig on 26 Mar 2011
I don't know what kind of extrapolation is done in Simulink, but have you looked on the FEX? This might help, for example:
jose tapia on 31 Mar 2011
INTERPNE doesn't work for me, because the data I have doesn't fit with the function.

Titus Edelhofer on 22 Nov 2011
Hi Jose,
in a German forum I gave a description on how the interpolation of Simulink works, see here, although I don't have a working solution. If you care for how the extrapolation works, I would translate here.
Titus
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Ilham Hardy on 16 Apr 2015
Hi Titus,
I know it is four years ago, but would you please describe how the 2D-LUT in Simulink works? This time in English?
I check the link you gave and translate it, but still I don't get it yet. The solution post by Jette is not complete (I mean ZI_1 is still matrix).
Thanks a lot, Ilham

Mehmet Özdemir on 13 Jun 2018
Hi everyone,
I was struggling with the same problem for some time and finally found a very easy solution. Save the date.
INPUT PARAMETERS
x = Column indicator of the matrix
y = Raw indicator of the matrix
v = Look up table matrix
xq, yq = Point where interpolation takes place
THE CODE
vq1 = interp1(x,v',xq,'linear','extrap') % This calculation gives an array which are the interpolated values (wrt xq) of every raw. PS : Don't forget to take the transpose of v matrix.
vq = interp1(y,vq1,yq,'linear','extrap') % This part interpolates the new calculated vq1 for the value yq and gives the final result
Since it is possible to extrapolate by adding ///,'linear','extrap'/// in this method, your task of extrapolating 2d maps will be accomplished. Good by NaNs.
Best
hang x on 28 Jul 2020
It's a nice way to solve this problem,thanks for sharing it