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I have simple Manipulation expression, but continuously getting error

Coordinate {x[0.], y[0.]} should be a pair of numbers, or a Scaled or Offset form.

I assume that something is wrong with Graphics, but don't know why Evaluate doesn't give numerical values.

The expression is:

Manipulate [{
     sx = NDSolve[{x''[t] + (2 k1)/m  (x[t] - a) == 0, x[0] == x0, x'[0] == vx0}, x[t], {t, 0, 10}];
     sy = NDSolve[{y''[t] + (2 k2)/m  (y[t] - a) == 0, y[0] == y0, y'[0] == vy0}, y[t], {t, 0, 10}];
     Graphics[{Disk[{Evaluate[x[tl] /. sx][[1]], Evaluate[y[tl] /. sy][[1]]}, 0.1]}, {PlotRange -> 6}]
     }[[1]], 
    {a, 1, 10}, {m, 1, 10}, {k1, 1, 100}, {k2, 1, 100}, {x0, 0, 10}, {y0, 0, 10}, {vx0, 2, 10}, {vy0, 2, 10}, {tl, 0, 10}
]
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5
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Manipulate[{sx = NDSolve[{x''[t] + (2 k1)/m (x[t] - a) == 0, x[0] == x0, x'[0] == vx0},
                 x[t], {t, 0, 10}];
   sy = NDSolve[{y''[t] + (2 k2)/m (y[t] - a) == 0, y[0] == y0, y'[0] == vy0}, 
                y[t], {t, 0, 10}]; 
   Graphics[{Disk[{Evaluate[x[t] /. sx][[1]],  Evaluate[y[t] /. sy][[1]]}, 0.4]},
            PlotRange -> 6] /. t -> tl}[[1]],
 {a, 1, 10}, {m, 1, 10}, {k1, 1, 100}, {k2, 1, 100}, {x0, 0, 10},
 {y0, 0, 10}, {vx0, 2, 10}, {vy0, 2, 10}, {tl, 0, 10}]

enter image description here

To get a hint as to why the original code does not work, try

Evaluate[y[t] /. sy]
(* {InterpolatingFunction[{{0.`,10.`}},"<>"][t]} *)

and

Evaluate[y[tl] /. sy]
(* {y[tl]} *)

Similarly, for x[t].

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  • $\begingroup$ Simple. Thanks. $\endgroup$ – tobix10 Oct 10 '14 at 16:31

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