expression will only start at the beginning of an animation

Question

Hello, I am using this expression;

freq = 1.0; //oscillations per second
amplitude = 50;
decay = 0.7;

amplitude*Math.sin(freq*time*2*Math.PI)/Math.exp(decay*time)

From this source (the pendulum with decay); http://www.motionscript.com/mastering-expressions/simulation-basics-3.html

I need this expression in the middle of my animation, however, it will only play the animation at the very beginning of my timeline, no matter where I place they keyframes.
I also tried duplicating the asset with crtl+shift+d so that the animation might start at the split, however this did not work and the animation still played from the beginning, but since the beginning of the animation was cut off, it just resumed in the middle of the animation where the cut was instead of playing the whole expression.
Why is this happening, and how can I fix it?

Dan Ebberts · Accepted Answer

It depends on how you want to tell it when to start. If you know the time, you could do it like this (it will start at 2 seconds in this example):

tStart = 2;
freq = 1.0; //oscillations per second
amplitude = 50;
decay = 0.7;
t = Math.max(time - tStart,0);
amplitude*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t)

Dan

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