Function Description
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	Name: Z_D_MELT 
	Function: Pierre Lavigne's dimer melt function 
	Parameters: a0 a1 a2 a3 a4 a5 a6 a7

Notes
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D_MELT: model to fit temperature denaturation of a dimeric protein

NOTE: The temperature must be in celcius. 

a0= mean residue ellipticity for the N state @ 0oC
a1= constant slope for the temperature dependance
    of the mean residue ellipticity of the N state
a2= mean residue ellipticity for the N state @ 0oC
a3= constant slope for the temperature dependance
   of the mean residue ellipticity of the N state
a4= DHu (kcal/mol)
a5= DCp,u (temperature independent, kcal/K mol)
a6= Tm (K)
a7= concentration (M)


C-code for the function
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 b = x + 273.15;
 c = b*((a[4] / a[6]) + a[5] * log(b/ a[6]) + 0.001987 * log(a[7]));
 d = a[4] + ( a[5] * (b - a[6]));
 e = d - c;
 f = exp((-e) / (b * 0.001987));
 g = (-f + sqrt((f*f) + 8.0 * a[7] * f)) / (4.0 * a[7]);
 answer = (1.0 - g) * (a[0] - a[1] * x) + g * (a[2] - a[3] * x);