# How to plot the answer obtained from NDSolve

cf = 200000000;
α = .7;
r = 0.4;
g0 = 1;
g1[t_] := g0 Sin[t/τ];
g2[t_] := -g0 Cos[t/τ];
γc1 = 000 Pi;
γc2 = 000 Pi;
γf = 44000 Pi;
τ = 1;
ξi = {{Re[α]}, {Im[α]}};
ai = {{E^(-2 r), 0}, {0, E^(2 r)}};
hassan = Table[{L, FSR = Pi (cf/L);
γ1 = (2 γf g1[t]^2)/FSR;
γ2 = (2 γf g2[t]^2)/FSR;
γ12 = (2 γf g1[t] g2[t])/FSR;
sol1 =
NDSolve[{m1'[t] == (-γc1 + γ1/2) m1[t] -
g1[t] f0[t] - γ12/2 m2[t],
f0'[t] == -(γf/2 f0[t] + g1[t] m1[t] + g2[t] m2[t]),
m2'[t] == (-γc2 + γ2/2) m2[t] -
g2[t] f0[t] - γ12/2 m1[t], m1[0] == 1, f0[0] == 0,
m2[0] == 0}, {m1, m2, f0}, {t, 0, (Pi/2 ) τ}];
MM[t_] = Evaluate[m2[t] /. sol1[[1]]];
ans = MM[(Pi/2) τ];
ξf = (ans) ξi;
af = (.75) (ans^10) (ai);
ξ1 = ξi - ξf;
ξT1 = Transpose[ξ1];
det = Det[ai + af];
inv = Inverse[ai + af];
zarb1 = ξT1.inv.ξ1},
{L, 1, 1000, 100}]
ListPlot[hassan]
{{1, {{1.09029}}}, {101, {{1.06622}}}, {201, {{1.04201}}}, {301, \
{{1.01766}}}, {401, {{0.993172}}}, {501, {{0.968559}}}, {601, \
{{0.943825}}}, {701, {{0.91898}}}, {801, {{0.89403}}}, {901, \
{{0.868985}}}}


I have some differential equations as below. I have tried to solve them numerically with NDSolve and to plot zarb1 versus L. what's the problem I want to plot hassan versus L.

The matrix product ξT1.inv.ξ1 gives a $1\times 1$ matrix. In order to turn it into a scalar replace the last line in the first argument of the Table with (ξT1.inv.ξ1)[[1,1]] and your plot should work.