function ixfind, z,val,del
;
; Find nearest index to val in z, with increment del
; If not found, return -1
;
nz = n_elements(z)
if del gt 0 then begin
  for i=0,nz-1 do begin
    if (val ge z(i)-0.5*del and val le z(i)+0.5*del) then return,i
  endfor
endif else begin
  for i=0,nz-1 do begin
    if (val eq z(i)) then return,i
  endfor
endelse
return,-1
end