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NDolve + ParametricPlot


Hi, i'm new with Mathematica..i'm getting mad with expressions like this:

sol = NDSolve[{x''[t] == x[t], x[0] == 1, x'[0] == 1.1}, x, {t, 0, 3}];
Plot[x[t] /. sol, {t, 0, 3}];
Plot[D[x[t]] /. sol, {t, 0, 3}];
ParametricPlot[Evaluate[{x[t] /. sol, D[x[t] /. sol]}], {t, 0, 3}];

The first two Plots are ok, the third give me:



ParametricPlot::pptr: {InterpolatingFunction[{{0., 3.}}, {2, 2, True,
Real, \
{3}, {0}}, {{\[LeftSkeleton]1\[RightSkeleton]}}, {{0, 3, 6, 9, 12, 15, 18, \
21, 24, 27, \[LeftSkeleton]32\[RightSkeleton]}, {1., 1.1, \[LeftSkeleton]8\
\[RightSkeleton], \[LeftSkeleton]113\[RightSkeleton]}}, {Automatic}][t]}
does \
not evaluate to a pair of real numbers at t = 1.25`*^-7.




... and "More..." does tell nothing more.

Where is my mistake?

Thanks and sorry for my bad english

Paolo


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