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if ?plist(fft)=false then loadfile(fft,fasl,dsk,share)$
if ?plist(fillarray)=false then loadfile(array,fasl,dsk,share)$
/* set up arrays */ array([g,h,xa],float,31)$
(fillarray(g,[0.0]),fillarray(h,[0.0]),
for i from 0 thru 15 do g[i]:1.,
for i from 0 thru 31 do xa[i]:float(i))$
/* define function to display them */
p():=plot2d([[discrete,listarray(xa),listarray(g)],[discrete,listarray(xa),listarray(h)]])$
p()$
/* perform fft */ fft(g,h)$
p()$
/* put in polar form */ recttopolar(g,h)$
p()$
/* undo these operations */
polartorect(g,h)$
p()$
ift(g,h)$
p()$
/* if you want avoid having the transform done in place,
copy the arrays first */
(fillarray(g,[0.0]),fillarray(h,[0.0]),
for i from 0 thru 15 do g[i]:1.)$
array([gt,ht],float,31)$
(fillarray(gt,g),fillarray(ht,h))$
fft(gt,ht)$
plot2d([[discrete,listarray(xa),listarray(gt)],[discrete,listarray(xa),listarray(ht)]])$
/* The last part of this demo plots pretty patterns created by FFT.
They will only look good if your terminal supports high resolution
plotting. If it doesn't I suggest you quit out here by typing
^G. This function was pinched out of some magazine put
out by Tektronix a year or two ago. */
pl&&
plinit(nn):=(block([i:?runtime()],?sstatus(?random,i)),
array([fr,fi],float,2**nn-1),n:nn)$
plinit(8)$
pl():=block([xaxis:false,yaxis:false,noprint:true,
dateplot:false,equalscale:true],
apply (rearray, ['fr, 2^n - 1]),
apply (rearray, ['fi, 2^n - 1]),
fillarray(fr,[0.0]),fillarray(fi,[0.0]),
thru 2 do if random(2)=0
then fr[random(2**n)]:(-1.0)^random(2)
else fi[random(2**n)]:(-1.0)^random(2),
fft(fr,fi),
graph2([fr,[fr[0],fr[2**n-1]]],[fi,[fi[0],fi[2**n-1]]]))$
thru 10 do pl()$
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