what about doing something like this, for a half sine:
A = - 9.8e6 ! amplitude
xtime=.0001 ! seconds
ttime=.0001*3
asize=75 ! data resolution
pi=3.141592654
*dim,xdata,table,asize,1,1,time
xdata(1)=0.0
xdata(1,0)=0.0
*afun,rad
*do,i,2,asize
xfr=pi*(i/asize)...