How to load a big .txt-file while using ode45

Question

Hekseli 2013-9-27

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/88439-how-to-load-a-big-txt-file-while-using-ode45

回答： Hekseli 2013-9-27

Hey!

I am solving a differential equation system with ode45 solver and the problem is that one of the derivatives demands a constant parameter from a big matrix (5x500000), depending on the previous step values in vector x. I can't load the matrix in a differential equation function because then it will be called multiple times and loading takes time.

So where / how should I load this big matrix?

A quick example would be something like this.

function1

[T, X]=ode45(@differ,[0 1],[1 1 1 1]); plot(X(:,1),X(:,2)); hold on;

end

function f = differ(t, x) %x=(x1 x2 x3 4)

A=load('file.txt'); %Now this is not efficient g=9.81;

f = zeros(4,1); f(1) = x(3); f(2) = x(4); f(3) = 0; f(4) = -g*A(i,j); %Here i and j will be determined according to values in x(1) and x(2)

end