Lagrange polynomial: two equivalent m-files

Jan
2022 12 23
1 个回答
更新时间：2022 12 23
8 次查看（30 天）

0 个投票

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 ??

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Torsten
Torsten 2022-12-23
编辑：Torsten 2022-12-23
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
Jan 2022-12-23
编辑：Jan 2022-12-23
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
Torsten 2022-12-23
编辑：Torsten 2022-12-23
lagrangepoly.m is saved in your working directory ?
Jan
Jan 2022-12-23
I see. Now it works fine. I'm new to Matlab thus appologizing my confusion.Thank you.

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回答（1 个）

the cyclist
the cyclist 2022-12-23

0 个投票

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.

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