subr bisect,w,y,wb,yb
;find the min point and min and max range in y
iq=minloc(y)
iq=iq(0)
yb=findgen(101)/100.
yb=yb*(max(y)-min(y))+min(y)
ymin=min(y)     ymax=max(y)
nw=dimen(w,0)
;get min of the 2 sides at least
mq=max(y(0:iq))         mq=mq<max(y(iq:*))
yb=sieve(yb,yb lt mq)
x1=polate(y(iq:*),w(iq:*),yb)
x2=polate(reverse(y(0:iq)),reverse(w(0:iq)),yb))
wb=.5*(x1+x2)
endsubr