Re: interp1 - bug

[Roberto Abuter]

I am sorry for the double posting, I am very new to this list.
Indeed, X is not monotonically increasing and I now see in the Octave 
function description that X has to be monotonic.
Sorry for missing that !
I guess it is just a difference in behavior between Matlab and Octave.
one can always reshuffle (X,Y) in such a way X becames monotonic.

many thanks again,
Roberto AButer

John W. Eaton wrote:

> On 12-Sep-2009, Roberto Abuter wrote:
>
> |    I am using the most basic form of interp1 in both matlab and octave.
> |    To my surprise interp1 in octave (3.0.2)  is producing some very 
> | strange results on my data.
> | 
> |    I have a set of two vectors X, Y where X has a sawtooth shape (4 
> | repetitions) and Y has 4 repetitions of an increasing/decreasing 
> | amplitude sine wave.
> |    to start very simple I just check the interp1 engine by making :
> |   
> |    XI = X;
> |    YI = interp1(X,Y,XI)
> | 
> | 
> |    to my surprise, the result YI  comes out not identical to Y .  
> |   
> |    well, if I try to interp1 with XI as my target grid ( a regular one 
> | ) I get absolutely wierd results.
> | 
> | hope someone can give me a hint.
>
> Is X monotonically increasing (or decreasing)?  From your description
> it sounds like it is not.
>
> If you think you've found a bug, then please include enough
> information so that someone can reproduce precisely what you are
> doing and report it to address@hidden
>
> In any case, there is no need to cross post to both the bug and help
> lists.
>
> jwe
>