# how to use interp1() function

92 vues (au cours des 30 derniers jours)
zein le 12 Fév 2020
Modifié(e) : Stephen23 le 12 Fév 2020
I have tried to use interpt(1) function as i have time and pressure data.
the pressure data is highly scattered it look like that
firstly,I have used function : p0q=interp1(p0,tq) as show belows
_____________________________________________________________________________________
t1=t(x1:x2);
p01=p0(x1:x2);
tq=t(x1):0.000001:t(x2);
p0q=interp1(p0,tq);
figure
plot (t1,p01,'o',tq,p0q,'*');
legend('p01','p0q');
_____________________________________________________________________________________
but the poq (interpolated result is empty) as shown in the figure
when i change it to
p0q=interp1(p0,tq,'pchip');
the interploted data are incorrect
is there something wrong in my code?or i am using the function incorrectly?
##### 1 commentaireAfficher -1 commentaires plus anciensMasquer -1 commentaires plus anciens
KSSV le 12 Fév 2020

Connectez-vous pour commenter.

### Réponse acceptée

Stephen23 le 12 Fév 2020
Modifié(e) : Stephen23 le 12 Fév 2020
The problem is that you are using the default x values, which for a vector input are defined as
1:numel(v)
These default points only make sense if you are also requesting interpolation for x>=1 and x<=numel(v), but look at the x points you are requesting interpolation at: judging by your screenshot they are somewhere between 0.06162 and 0.06067. The points you are requesting lie nowhere close to the the input x values (for which you used the default values 1:numel(v), and which iare thus totally unsuitable for your task).
The solution is simple: you need to provide the input x values, i.e.:
p0q = interp1(t1, p0, tq);
##### 1 commentaireAfficher -1 commentaires plus anciensMasquer -1 commentaires plus anciens
zein le 12 Fév 2020
Modifié(e) : zein le 12 Fév 2020
yes,I wrote the line incorrectly, it should be writtien like that
p0q=interp1(t1,p01,tq,'linear');

Connectez-vous pour commenter.

### Catégories

En savoir plus sur Multirate Signal Processing dans Help Center et File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by