[問題] 解常微分方程

[mgla8063 (青澀的柿子)]

我要解一個聯立微分方程：

    x'=0.02x-0.00004xy
    y'=0.0004xy-0.04y
    x(0)=500
    y(0)=200

其中x,y都是t的函數，我輸入下面的指令：

DSolve[{x'[t] == 2/100 x[t] - 4/100000 x[t] y[t],
        y'[t] == 4/10000 x[t] y[t] - 4/100 y[t], y[0] == 200, x[0] == 500},
        {x[t], y[t]}, t]

卻發現電腦給我一大堆錯誤訊息，

想請問是哪裡出了問題？謝謝大家。

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推 Frobenius:Solve::ifun: Inverse functions are being used by
→ Frobenius:Solve, so some solutions may not be found; use
→ Frobenius:Reduce for complete solution information. (出現三次)
推 Frobenius:General::stop: Further output of Solve  will be
→ Frobenius:suppressed during this calculation.
推 Frobenius:DSolve::bvnul: For some branches of the general
→ Frobenius:solution, the given boundary conditions lead to
→ Frobenius:an empty solution.                        (出現兩次)