How can I solve this ODE 1000 times with random variables?

3 次查看（过去 30 天）
Thomas Veith
Thomas Veith 2019-5-30
评论： Star Strider 2019-5-30
So I have this code:
tspan=[1 7];A0=rand;P0=rand;g=rand;p=rand;B=rand;
[t,x] = ode45(@(t,x) [-g*x(1) + p*x(1); -x(1)*x(2)+ B*x(2)], tspan, [A0 P0])
And it works perfectly.
But what I want to do is run it 1000 times and change the random inputs each time, and generate new solutions every time. I've tried using the following:
n = 1000;
result = zeros(n,1);
for k=1:n
tspan=[1 7];A0=rand;P0=rand;g=rand;p=rand;B=rand;
[t,x(n)] = ode45(@(t,x) [-g*x(n(1)) + p*x(n(1)); -x(n(1))*x(n(2))+ B*x(n(2))], tspan, [A0 P0])
result(k) = x(n);
end
But I get the error
Index exceeds the number of array elements (2).
Error in @(t,x)[-g*x(n(1))+p*x(n(1));-x(n(1))*x(n(2))+B*x(n(2))]
Error in odearguments (line 90)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode45 (line 115)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Any advice?
  1 个评论
Thomas Veith
Thomas Veith 2019-5-30
Alternatively, if I try this:
n = 1000;
result = zeros(n,1);
for k=1:n
tspan=[1 7];A0=rand(n);P0=rand(n);g=rand(n);p=rand(n);B=rand(n);
[t,x] = ode45(@(t,x) [-g*x(1) + p*x(1); -x(1)*x(2)+ B*x(2)], tspan, [A0 P0])
result(k) = x(n);
end
I get the following error:
Error using odearguments (line 93)
@(T,X)[-G*X(1)+P*X(1);-X(1)*X(2)+B*X(2)] must return a column vector.
Error in ode45 (line 115)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Star Strider
Star Strider 2019-5-30
You coded your differential equation correctly. Your ‘x’ variable has only two elements, so you cannot use ‘n’ (or ‘k’) to subscript them.
See if this does what you want:
n = 1000;
result = cell(n,1);
for k=1:n
tspan=[1 7];A0=rand;P0=rand;g=rand;p=rand;B=rand;
[t,x] = ode45(@(t,x) [-g*x(1) + p*x(1); -x(1)*x(2)+ B*x(2)], tspan, [A0 P0]);
result{k} = x;
end
Note that because the time vector can change between your ode45 calls, a cell array is most appropriate. If you want a specific number of values to be returned each iteration, define ‘tspan’ as a vector of more than two elements.

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Ordinary Differential Equations 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by