;
function ixfind_nearest,z,val
nz = n_elements(z)
;print,'ixfind_nearest: nz=',nz,' z=' & print,z
if val ge z[nz-1] then return,nz-1
if val le z[0] then return,0
for i=1,nz-2 do begin
  if val le 0.5*(z(i)+z(i+1)) and val ge 0.5*(z(i)+z(i-1)) then begin
    return,i
  endif
endfor
return,-1
end