Lagrange polynomial: two equivalent m-files

I have a problem with the Lagrange polynomial in Matlab.

Here they write

% YY = LAGRANGEPOLY(X,Y,XX) returns the values of the polynomial

% sampled at the points specified in XX -- the same as

% YY = POLYVAL(LAGRANGEPOLY(X,Y)).

%

I understand that XX are the points at which the Lagrange polynomial is evaluated. But the the command after the second YY doesn't contain XX. So why these two YY are the same ? How can they be the same ??

[Torsten]

Must read:

YY = polyval(lagrangepoly(X,Y),XX)

instead of

YY = polyval(lagrangepoly(X,Y))

But why don't you simply run the code with the example provided ?

[Jan]

Sounds good. But I'm getting these errors, neither possibility works:

>> YY = polyval(lagrangepoly([1,2],[3,4]),[1])
Unrecognized function or variable 'lagrangepoly'.
 
>> YY = polyval(Lagrang([1,2],[3,4]),[1])
Error using Lagrang
Too many output arguments.
 

[Torsten]

lagrangepoly.m is saved in your working directory ?

[Jan]

I see. Now it works fine. I'm new to Matlab thus appologizing my confusion.Thank you.

Answer 1

[the cyclist]

Assuming you are talking about this submission to the FEX, it is not from Mathworks. It is a user-contributed function. I guess you'd need to ask the author what they meant.