msci Code

;inverts a function through bisection:
function bisect, fname, x1, x2, tol=tol, params=params

  if n_elements(tol) ne 1 then tol=0.0001

  f1=call_function(fname, x1, params=params)
  f2=call_function(fname, x2, params=params)

  xmid=(x1+x2)/2

  f0=call_function(fname, xmid, params=params)

  ;while abs(f0) gt tol do begin
  while abs(x1-x2) gt tol do begin
    if f0 lt 0 then begin
      f1=f0
      x1=xmid
    endif else begin
      f2=f0
      x2=xmid
    endelse
    xmid=(x1+x2)/2
    f0=call_function(fname, xmid, params=params)
  endwhile

  return, xmid
end