Use of interp2 in an arbitrary dataset (2024)

Thank you for your response but to my understanding, scatteredInterpolant does not allow the use of spline, cubic or makima functions? Am I right? If so, is there a workaround to use particularly spline or makima?

Thanks

Stathis

You have 3 data points, on a 2D surface. That is the minimum number needed to define a plane (assuming they are not collinear). With so few points, you cannot estimate a more sophisticated surface, such as a spline. You would need at least 4 points (2 in each dimension) to use makima and at least 16 (4 in each dimension) to use spline. With only three points, linear interpolation is your only option.

Thank you @William Rose for your response. I wasnt actually aware of this requirement for spline and makima.

My dataset will generally be small but it will vary from 3 up to 11-12 points. You are saying that makima would need 4 points. Therefore, if the original dataset as an example has the following 4 points, how could I use makima or cubic?

x=[0.25;0.50;0.75;0.9];

y=[0.25;0.60;0.35; 0.7];

Z = [0.5; 1.5; 3.0; 3.5];

Thanks

If your data are not gridded, you will have to live with "ScatteredInterpolant" and its interpolation methods.

And your four points in 2d constitute a curve. So Z could be interpolated on this curve maybe, but it makes little sense to treat them as sufficient to interpolate on a real two-dimensional rectangle.

You already interpolate (extrapolate) when you assume that (x,y,z) can be extended to (X,Y,Z) as existing database for interpolation with interp2.

Dear @Sulaymon Eshkabilov, thanks for your response which seems to work fine but you have made a mistake in your Data matrix and this seems to make a difference.

In particular, the 3rd element in the y vector should be 0.35 and not 0.75.

When I try to use 0.35 with your version of the code, I get:

Error using griddedInterpolant

Sample points must be sorted in ascending order.

Error in interp2>makegriddedinterp (line 226)

F = griddedInterpolant(varargin{:});

Error in interp2 (line 134)

F = makegriddedinterp(X, Y, V, method,extrap);

Is there a workaround for this error?