Bulk Modulus

read a file like (E(eV) vis a(Ang) ):
x1 y1
x2 y2
x3 y3
x4 y4
. .
. .
. .
. .

We use:
y=b0 + b1*x +b2*x**2
with:
add(x**0)*b0 + add(x**1)*b1 + add(x**2)*b2 = add(y)
add(x**1)*b1 + add(x**2)*b2 + add(x**3)*b3 = add(yx)
add(x**2)*b2 + add(x**3)*b3 + add(x**4)*b4 = add(yx**2)

if opt = true then the program use only the points
that do (RMS > 0.01)


We have used:
V=a³*beta
B0=-V*dP/dV = -a/3 * dP/da
P=dE/dV=-dE/da*1/(3*a²beta)
E=Aa²+Ba+C
B0=2/(9a²beta)*(2Aa+B)+1/(9a*beta)*2A
B0=[ 2/(9a²beta)(2Aa+B)+2A/(9a*beta) ]*160.2177 GPa