"Invalid interpolation method" after moving to MATLAB2020b

This code was working well using MATLAB2018a:

z_t = interp1(time,x,y,'splines')

In MATLAB2020b, it is showing these error:

Error using interp1>sanitycheckmethod (line 285)

Invalid interpolation method.

Error in interp1>parseinputs (line 393)

method = sanitycheckmethod(last);

Error in interp1 (line 112)

parseinputs(X,V,penultimate,last,nargin,ndataarg,pp);

[Star Strider]

Andrea Pirlo — See my Answer (and Vote for it if it solves your problem)!

Answer 1

[Star Strider]

See method in the interp1 documentation (R2020b, however I doubt if it’s changed significantly since R2018b).

[Yousef Dajani]

It looks like there was a typo: "spline" instead of "splines".

Weird that it ran on MATLAB2018a!

Anyway, I corrected the typo. Thanks for your answer!

[Star Strider]

As always, my pleasure!

[John D'Errico]

My guess is if it worked in the past, they changed something, making it slightly more picky.

The property has always been just 'spline' as far back as I can remember. Therefore, this was arguably a bug fix, making the code consistent with the documenttion, and as the docs have always been.

[Steven Lord]

I would have to go back and check but I suspect the refactoring that improved performance in release R2020a brought with it stricter input argument checking.

[Will Reeves]

In my case I see an error with "linear" interpolation but see the same error message:

pp = interp1(x,v,'linear','pp');

I've just had to resurrect some old code, and find it irratating that seemingly basic functionality has changed even though I've changed nothing. What's particularly unhelpful is the lack of good quality error messages. "Invalid interpolation method". Well, it used to work, and it seems as though the documentation hasn't changed from my usage so what is the problem?

I do notice that there is an "orange squiggle" hinting that using piecewise polynomial is "not recommended" and to use "griddedInterpolant" instead though.

______________________________________

Hilarious! I made exactly the same mistake... nearly... I wrote "liner" and not "linear"! Apologies!

[Walter Roberson]

@Will Reeves looks to me as if it works

x = 1:5;
v = rand(1,5);
pp = interp1(x,v,'linear','pp');
pp

pp = struct with fields:
      form: 'pp'
    breaks: [1 2 3 4 5]
     coefs: [4x2 double]
    pieces: 4
     order: 2
       dim: 1
    orient: 'first'

[Will Reeves]

Hi, yes it does... but not when you spell "linear", "liner" (like I did!) - although it's interesting that it used to work. Perhaps the function just used to compare the first few letters of the method or something. Anyway, it was my fault! Apologies!