Vector input for ODE45

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Oday Shahadh 2017-2-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/326304-vector-input-for-ode45

评论： Walter Roberson 2017-2-23

Sirs, I have something like the below formula:

T=(A+B+C)+(D*T) dt where A, B and C are vectors with let me say (1,6000) length How Can I integrate this formula using ODE45, please help, and thanks in advance

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Walter Roberson 2017-2-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/326304-vector-input-for-ode45#answer_255834

在 MATLAB Online 中打开

   x0 = ... something same length as A;
   [T, X] = ode45( @(t, x) f(t, X, A, B, C, D), tspan, x0);
function dy = f(t, y, A, B, C, D)
  dy = (A + B + C) + (D*t);

... except of course if that were really your formula you would construct

    x0 = ... something same length as A;
    ApBpC = A + B + C;
   [T, X] = ode45( @(t, x) f(t, X, ApBpC, D), tspan, x0);
function dy = f(t, y, ApBpC, D)
  dy = ApBpC + (D*t);

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Oday Shahadh 2017-2-23

how to develope the loop? to avoid overwriting a previues values?

Walter Roberson 2017-2-23

在 MATLAB Online 中打开

i_vals = 1 : 10 : t;
num_i = length(i_vals);
Tdot = zeros(num_i, 1);
for i_idx = 1 : num_i
  i = i_vals(i_idx);
  Tdot(i_idx) = A(i) + B(i) + C(i) - T;
end
result = TDot;

Note that the resulting value changes length as t increases. If t represents the time parameter to the ode, then this would mean that you are trying to return a different number of derivatives as time goes on.

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