2D LUT (extrapolation) Simulink vs interp2

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?

[Ilham Hardy]

Another angle:

Is there anyway to retrace the calculation done by 2D-lookup table in Simulink? Does 2D-LUT block calls specific Matlab function?

Answer 1

[Sebastian Castro]

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

[Ilham Hardy]

Sebastian,

I am not quite sure that I get your point. If i understand correctly, the 'scalar' argument is actually one scalar number/constant to replace NaN when interp2 extrapolates. It doesn't really extrapolates.

What I need, or what the 2D lookup table does , is actually a 2D extrapolation instead of returning NaN or just one scalar number.

[Sebastian Castro]

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]

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.