Function biexp(w,x)
  Wave w; Variable x

  Variable a0,a1,k1,k2 
   Variable g0,g1,g2

   a0 = w[0]
   a1 = w[1]
   k1 = w[2]
   k2 = w[3]
 
   g0 = a0
   g1 = exp(-k1*x)
   g2 = exp(-k2*x)
   return g0+a1*(-g1+g2)
End