Hello, I understand the basic structure of DifferentialEquations but what if the equations you would like to use do not fit neatly like function lorenz(du,u,p,t) du[1] = 10.0*(u[2]-u[1]) du[2] = u[1]*(28.0-u[3]) - u[2] du[3] = u[1]*u[2] - (8/3)*u[3] end For example, the equations I need to use…

Hello Everyone, I am back with a functioning code that generates differential equations. Wooo! :relieved: Apologies if any of this seems obvious, but the things I learned along the way (in case anyone else struggling is reading this): Making something a constant (const) even if the value changes, …

I’m not sure where the confusion is. The function passed to diffeq can do anything it likes, including calculating intermediate things like F_ij. You can pass in a p, which can be any type you like, to hold your parameters. Maybe looking at GitHub - SciML/SciMLTutorials.jl: Tutorials for doing …

[image] HelgavonLichtenstein: For example, the equations I need to use (1,2) could be written to fit within DifferentialEquations structure, but I would be unable to list the parameters (3,4 ect) neatly since they refer to other variables You can always pass additional parameters to a functio…

[image] stevengj: Because of this, I think DifferentialEquations didn’t really need an explicit p argument f(x, p, t) in its basic ODE interface, since parameters could have been passed using closures. My guess is that @ChrisRackauckas defined it this way to make it easier to support parameter e…

Hello again, I have tried for several days to understand your responses but I feel I am not closer to understanding what is meant by your advice. In the hope that I can calculate differential equations with more complicated equations, my code snippet looks like this (full code is at the end). usi…

Don’t use the macro here. Just define a function. This part of the tutorial shows how to do this: http://docs.juliadiffeq.org/latest/tutorials/ode_example.html#Example-2:-Solving-Systems-of-Equations-1 Or maybe some of the examples here would be good to follow: https://nbviewer.jupyter.org/github…

Thank you for your reply. I’ve changed the code snippet, but I get a method error at du[1] = function Basal(r,B,K,Feeding). I am still unclear on whether I can have a function within a differential equation function. ERROR: MethodError: Cannot `convert` an object of type getfield(Main, Symbol("#Ba…

I have no idea what you’re doing with those inner anonymous functions. You may want to follow the tutorials to see the proper syntax.

It seems like a lot of your confusion is related to defining and calling functions, not from DifferentialEquations. In your last example, you are assigning a function object (a.k.a. an anonymous function) to the elements of the vector du, which is not what you want. I’m guessing what you want to d…

Perhaps it is somewhat difficult to give you a straight answer to your questions because it is not totally clear what you try to do/what your models do. At least not to me. You present 4 equations. Equations (1) and (2) seem to be balance equations for some quantity B_i. Is index i in B_i the spec…

Hello again, I re-did many things with the code and chose a different paper to base my formulas on. I want to thank everyone who commented so far - this is a learning process and hopefully I did not cause too many headaches. Based on @ElOceanografo 's example, a snippet of code now looks like: usi…

How to use DifferentialEquations with complicated equations

New to Julia

Tamas_Papp May 9, 2019, 10:33am 12

Having a self-contained example would make it much easier to reproduce the error and help you.

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How to use DifferentialEquations with complicated equations

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