Hello, Here is my Mathematica code :
eqn1 = a'[t] == b[t]
K = 0.0003
eqn2 = b'[t] ==
a[t]/(a[t]^2 + 1/a[t]^2) (2 b[t]^2/a[t]^4 + K r[t] a[t]^4 -
K/(r[t] a[t]^4))
eqn3 =
r'[t] ==
b[t] r[t]/
a[t] ((b'[t]/a[t] (a[t]^2 - 1/a[t]^2) +
2 b[t]^2/a[t]^4)/(K (a[t]^4 r[t] + 1/(a[t]^4 r[t]))) - 4)
s =
NDSolve[{eqn1, eqn2, eqn3, a[0] == r[0] == 1, b[0] == 400}, {a[t],
b[t], r[t]}, {t, 0, 3}, Method -> "BDF"]
Plot[Evaluate[r[t] /. s], {t, 0, 0.01},
PlotRange -> {{0, 0.005}, All}]
Plot[Evaluate[b[t] /. s], {t, 0, 0.05},
PlotRange -> {{0, 0.02}, All}]
Plot[Evaluate[b'[t] /. s], {t, 0, 0.02},
PlotRange -> {{0, 0.02}, All}]
r(t), a(t) and b(t) plot successfully but not b'(t) (nor a'(t) nor r'(t)) : I just get an empty graph without any error message! I have very little experience in Mathematica. Thanks in advance for any helpful advice and comments.
