Thread Subject: does anyone know a "faster" interp1?

Hi everyone,

I have a code in which I heavily use interp1 (with the pchip
option, btw). Does anyone know of a faster interp1? In the
File Exchange, I only found codes for linear or nearest
neighbor interpolation...

Thanks!!

PS: I really need to interpolate several times. So, I cannot
use pchip to get the polynomial and just evaluate it later on.

If your input vector is evenly spaced, use interp1q.

Alternatively, check the file exchange. 10 seconds of search
gives rise to the following:

http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=10286


(reconstruct the link if it gets broken)

Tom Clark

OK,

Sorry for being a fool... I'm scanning the newsgroup and
didn't notice the implications of your pchip requirement.
The above link won't be right for you.

If your input vector is evenly spaced, interp1q is still a
good bet.

Also, check whether there is any difference between the
following...

x = blah;
y = blah;
xi = blah_interp_points;

yi = pchip(x,y,xi)
% or
yi = interp1(x,y,xi,'pchip')

My understanding is that they're functionally the same, but
interp1 checks the inputs - so it may take longer to run.

Alternatively, try to think outside the box. I once had code
which unavoidably made a lot of 1D interpolations... I
re-jigged the code so that it did all the necessary
interpolations first, to a fine degree. I saved the lot to a
mat file. Then, whenever I re-ran my code, I just loaded the
mat file, and use linear interpolation on the finely spaced
data.

Keep the faith... there's always another way!

"Thomas Clark" <t.clarkremove_spam@cantab.net> wrote in message
<g4gvj6$flc$1@fred.mathworks.com>...
> If your input vector is evenly spaced, use interp1q.
>
> Alternatively, check the file exchange. 10 seconds of search
> gives rise to the following:
>
> http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?
objectId=10286
>
>
> (reconstruct the link if it gets broken)
>
> Tom Clark

But neither of these options offers a pchip
interpolation.

I don't know of any faster methods, although
is your data equally spaced? If so then a
pchip variant could be made more efficient
for that special case.

John

"John D'Errico" <woodchips@rochester.rr.com> wrote in
message <g4h0se$qso$1@fred.mathworks.com>...
> "Thomas Clark" <t.clarkremove_spam@cantab.net> wrote in
message
> <g4gvj6$flc$1@fred.mathworks.com>...
> > If your input vector is evenly spaced, use interp1q.
> >
> > Alternatively, check the file exchange. 10 seconds of search
> > gives rise to the following:
> >
> >
http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?
> objectId=10286
> >
> >
> > (reconstruct the link if it gets broken)
> >
> > Tom Clark
>
> But neither of these options offers a pchip
> interpolation.
>
> I don't know of any faster methods, although
> is your data equally spaced? If so then a
> pchip variant could be made more efficient
> for that special case.
>
> John

I'm afraid the data is not equally spaced...