Script: Indexing in function problem

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?

Answer 1

[Cris LaPierre]

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.

[Cris LaPierre]

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]

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.