Script: Indexing in function problem

1 vue (au cours des 30 derniers jours)
Norbert Raducki
Norbert Raducki le 22 Nov 2020
Commenté : Cris LaPierre le 26 Nov 2020
Hi,
I want to creat a function like this:
c(t+1,i)= c(t,i)-1/(dx^2)*(-D*(c(t,i+1)-c(t,i))-(-D*(c(t,i)-c(t,i-1)))) to solve this by ode4
and I do it like this:
but it dosen't work. I don't now why. Could someone explain to my why it dosen't work and how to indexing in fuction, pleace?

Réponses (1)

Cris LaPierre
Cris LaPierre le 22 Nov 2020
Modifié(e) : Cris LaPierre le 24 Nov 2020
Functions cannot be defined in the middle of your code. You will need to either place it at the bottom of your script, or in a separate file.
See this page for more.
  2 commentaires
Cris LaPierre
Cris LaPierre le 25 Nov 2020
Modifié(e) : Cris LaPierre le 25 Nov 2020
I could try to guess what your new code is, but it would be better if you shared your updated code first. Include the complete error message you are getting (all the red text), as well as what you are using for inputs to the function.
Cris LaPierre
Cris LaPierre le 26 Nov 2020
The error is because none of your if statements evalute to be true, so dcdt is neer assigned a value. This is because the conditional expression in an If statements only work with a single result. You define i to be a vector of numbers in your function, so it is returning a vector of results to the conditional expression.
if i is intended to be proportional to time, best to use t instead. If it is to try to collect your resutls, know that, with ode45, you do not have to worry about collecting the results of each iteration. This is handled automatically for you by the ode solver.
While not exactly the same, you may find this example helpful in setting up your problem.

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