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real*8 function voigt(a,v)
c******************************************************************************
c This routine calculates the voigt function using the approximations
c found in the *new series-astronomy and astrophysics* volume of
c landolt-bornstein.
c******************************************************************************
implicit real*8 (a-h,o-z)
a2 = a*a
v2 = v*v
if(a == 0.) go to 62
if(a <= 0.2) go to 50
if(a<=1.4 .and. a+v<=3.2) go to 30
c case 1, a .gt. 1.4 or (a .gt. 0.2 and a+v .gt. 3.2)
u = 1.4142136*(a2 + v2)
voigt = 0.7978847*a/u*(1.0 + (3.0*v2-a2)/u**2 + (15.0*v2*v2
1 -30.0*a2*v2+3.0*a2*a2)/u**4)
voigt = voigt/1.772454
return
30 u=0.979895023-0.962846325*a+0.532770573*a2-0.122727278*a*a2
31 h0 = dexp(-v2)
if(v >= 2.4) go to 35
if(v >= 1.3) go to 33
c case 2, 0.2 .lt. a .le. 1.4 and a+v .le. 3.2
h1=-1.12470432-0.15516677*v+3.28867591*v2-2.34357915*v*v2
1 +0.42139162*v2*v2
go to 36
33 h1=-4.48480194+9.39456063*v-6.61487486*v2+1.98919585*v*v2
1 -0.2204165*v2*v2
go to 36
35 h1=(0.554153432+0.278711796*v-0.188325687*v2+0.042991293*v*v2
1 -0.003278278*v2*v2)/(v2 - 1.5)
36 h2 = (1.0 - 2.0*v2)*h0
if(a <= 0.2) go to 52
h1 = h1 + 1.1283790*h0
h2p = h2
h2 = h2 - h0 + 1.1283790*h1
h3 = 0.37612635*(1.0-h2p) - 0.6666667*v2*h1 + 1.1283790*h2
h4 = 0.6666667*v2*v2*h0 - 0.37612635*h1 + 1.1283790*h3
voigt = u*(h0 + h1*a + h2*a2 + h3*a*a2 + h4*a2*a2)
voigt = voigt/1.772454
return
c case 3, a .le. 0.2 and v .lt. 5.0
50 if(v >= 5.0) go to 60
go to 31
52 voigt = h0 + h1*a + h2*a2
voigt = voigt/1.772454
return
c case 4, a .le. 0.2 and v .ge. 5.0
60 voigt = a/(1.772454*v2)*(1.0 + 1.5/v2 + 3.75/(v2*v2))
voigt = voigt/1.772454
return
c case 5, a .eq. 0.0
62 voigt = exp(-v2)/1.772454
return
end
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