function  XDIODE (xio,xk,v,slope)
implicit real *8 (a-h,o-z),   integer*4 (i-n)
real*8,  parameter  :: rmax=87.0d0  ! exp(rmax) ~ 6E+37
...
temp = xk*v
if (temp > rmax) temp=rmax
expt = xio *  exp (temp)
slope = xk * expt
diodq = expt - xio
XDIODE = diodq
end function  XDIODE
