You can use AnalyticCurve to draw curve directly.

Since you used

[code]

double u = _view.waveFunction.evaluate(x,t);

[/code]

to evaluate it's value in your code.

You can calculate u2=_view.waveFunction.evaluate(x,t-ddt);

And you can get du/dt with [u][color=red](u2-u)/[/color]ddt[/u] if [u]ddt[/u] is small enough!

Just calculated it by definition!

[/quote]

it was a brilliant idea/method but it didn't solve the problem :( It is because the code above is for the n = 50 points that is spread out in the x-axis, the little points.

original code from paco and wolfgang seems to use the %string% method to draw the nice function.

guess it is difficult to get du/dx = k*cos ( k*x - w*t) from a string u = sin ( k*x - w*t).

i go try your idea but on a separate loop.