Getting error while using interpolation function

While using interpoltaion function I am getting the follwing error.

*Undefined function 'interpl' for input arguments of type 'double'.

Error in interpolation (line 16) G=interpl(a,d,x); *

I wrote the code like this

t=[1:10]
 a=[0.1:0.1:1]
 d=[20:30]

x=0.45

    Y=interp1(a,t,x);
     G=interpl(a,d,x);

The code is working for 'Y', but if I added 'G' it is showing error.

What is wrong with my code?

Thanks

Answer 1

[John D'Errico]

Whats wrong? That you can't type? :)

I copied a piece of the error message that you got.

c = 'interpl'
c =
interpl

upper(c)
ans =
INTERPL

See that in the second call, you typed interpl, although you meant interp1. In fact, as soon as I saw the error, I knew this is what you had done. This is one of those mistakes you make once, then immediately know what to look for in the future, but it is difficult to debug.

[John D'Errico]

The funny thing is just recently, I warned someone against using the variable l (lower case L) and they replied scornfully how this was impossible, and would never cause a problem.

Depending on the font, 1 and l are just too close to be visibly different.

Best is often to use a display font that DOES distinguish those characters, to minimize the odds of these errors happening.

[R7 DR]

Hi

Thanks for the reply.

I used the same ''interp1'' for both Y and G.

I checked it again.

[R7 DR]

Now the error message is like this

Error using griddedInterpolant The grid vectors do not define a grid of points that match the given values.

Error in interp1 (line 183)
        F = griddedInterpolant(X,V,method);

Error in interpolation (line 16)
   G=interp1(a,d,x);

[John D'Errico]

The original error you got was ABSOLUTELY due to exactly what I said it was.

While you think you typed it properly, you did not. The error message that MATLAB gave repeated the name of the function you used.

"*Undefined function 'interpl' for input arguments of type 'double'."

What looks like a 1 in the function name is indeed a lower case L. MATLAB cannot lie.

Once you typed it properly, then a second error happens. The second error happens because a and t have 10 elements, so the first call works. But then the vector d has 11 elements.

You cannot form an interpolation mapping between the vectors a and d when a and d have a different number of elements. That would make no sense, so interp1 generates the error.

Had you used

d = 21:30;

the second call to interp1 (if spelled properly) would work with no problem.