interp1 vector of interpolated sample points using Euler method

1 view (last 30 days)
Hi, I have sompe tabular data that I have imported and have to interpolate between.
[date, t, Rainfall, Evap, I_t] = readvars("BOM_Data.xlsx");
% Define functions to allow interpolation of data
RAINFALL = @(time) interp1(t,Rainfall,time);
EVAP = @(time) interp1(t,Evap,time);
However when I use these values later on in the code it isnt working and those functions spit out NaN values for the first timestep.
For example, one of those equations is:
P_in(i) = RAINFALL(time(i)) *A_catch * C ;
Where A_catch and C are constant variables. The 2nd and further timesteps seem to work, however the 1st one is NaN, which flows on through to toher calcs and messes up others.
  1 Comment
Torsten on 13 Oct 2022
The t array from your Excel data must start with t(1) = 0. Is this the case ?

Sign in to comment.

Answers (1)

Jiri Hajek
Jiri Hajek on 13 Oct 2022
Please have a look into the documentation of interp1, namely the section on extrapolation method. You'll see that NaNs are the default result when you try to extrapolate, which is quite sensible.You have to check your input data and see whether you really want to extrapolate, as this is not really a typical task for an iterpolation method.
Jiri Hajek
Jiri Hajek on 13 Oct 2022
Perhaps you dont need it or want it, but it is the most straightforward explanation for the NaNs you are geting. You have to carefully check the inputs into the interpolator, that is all. You see, we do not know what are the values in your variables,you have to check them yourself...

Sign in to comment.




Community Treasure Hunt

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

Start Hunting!