I need to have a user input for a certain number of vectors to be created.

I have a vector of ODEs (ordinary differential equations) that I use to solve with the function ode45. My task is to have a user input of 'n' that calls for 'n' number of ODEs in my code. I know how to have the user prompt for 'n', I don't know how to make the program recognize that it needs to create 'n' equations in the function file. Any thoughts?

Right now it's hard-coded to 20 equations, but I need to have it to where user input determines number of equations. There is a recognizable pattern though.

Code for reference:

function [ DeltaO2Concentration ] = O2Solver_beta(t,O2Conc,c,O2Leak)
%UNTITLED Test function used to solve 'first attempt' code.
%   System of ODE diffusion equations that will be solved using 'ode45'
%   function. Inputs are constant composed of universal and calculated
%   constants, time (independent variable), O2Con (dependent variable), 
%   O2Leak which is a separate term or something.

%VECTOR LENGTH WILL NEED TO VARY ACCORDING TO USER INPUT%

DeltaO2Concentration = [0;
 c*t*(O2Conc(1)-O2Conc(2)+O2Conc(3)-O2Conc(2));
    c*t*(O2Conc(2)-O2Conc(3)+O2Conc(4)-O2Conc(3));
    c*t*(O2Conc(3)-O2Conc(4)+O2Conc(5)-O2Conc(4));
    c*t*(O2Conc(4)-O2Conc(5)+O2Conc(6)-O2Conc(5));
    c*t*(O2Conc(5)-O2Conc(6)+O2Conc(7)-O2Conc(6));
    c*t*(O2Conc(6)-O2Conc(7)+O2Conc(8)-O2Conc(7))+O2Leak;
    c*t*(O2Conc(7)-O2Conc(8)+O2Conc(9)-O2Conc(8))+O2Leak;
    c*t*(O2Conc(8)-O2Conc(9)+O2Conc(10)-O2Conc(9))+O2Leak;
    c*t*(O2Conc(9)-O2Conc(10)+O2Conc(11)-O2Conc(10));
    c*t*(O2Conc(10)-O2Conc(11)+O2Conc(12)-O2Conc(11));
    c*t*(O2Conc(11)-O2Conc(12)+O2Conc(13)-O2Conc(12));
    c*t*(O2Conc(12)-O2Conc(13)+O2Conc(14)-O2Conc(13))+O2Leak;
    c*t*(O2Conc(13)-O2Conc(14)+O2Conc(15)-O2Conc(14));
    c*t*(O2Conc(14)-O2Conc(15)+O2Conc(16)-O2Conc(15))+O2Leak;
    c*t*(O2Conc(15)-O2Conc(16)+O2Conc(17)-O2Conc(16));
    c*t*(O2Conc(16)-O2Conc(17)+O2Conc(18)-O2Conc(17));
    c*t*(O2Conc(17)-O2Conc(18)+O2Conc(19)-O2Conc(18)); 
    c*t*(O2Conc(18)-O2Conc(19)+O2Conc(20)-O2Conc(19));
    0];
end

Answer 1

[Steven Lord]

There's a recognizable pattern to the portions of your equations that involve the variable O2Conc. For that piece you probably could use the matrix generated by example 2 on the documentation page for the spdiags function. I don't see a pattern in which ODEs involve O2Leak and which don't.

[dpb]

"I don't see a pattern in which ODEs involve O2Leak"

I didn't either, but seems as though simply augmenting the array with

   O2Conc(sltnodes) = O2Conc(sltnodes) + O2leak;

should fixup the overall as he's passed the vector of locations. The question I've still got is just how many actual terms are supposed to be here...