用MMA画相曲线

本帖最后由青青子衿于 2021-7-7 22:14 编辑

StreamPlot[{x - y, 2 x}, {x, -3, 3}, {y, -3, 3}]
ParametricPlot[
Evaluate[#[t] & /@
   DSolveValue[{x'[t] == x[t] - y[t], y'[t] == 2 x[t], x[0] == #1,
   y[0] == #2}, {x, y},
   t] & @@@ {{1, -1}, {3, -2}, {4, -3}}], {t, -10, 10},
PlotRange -> 10]
https://paultallen.fun/2013/01/3 ... ferential-equations