Function i1ef_asympt 

fn i1ef_asympt(x: f32, sign_scale: f64) -> f32

Asymptotic expansion for I1.

Computes: sqrt(x) * exp(-x) * I1(x) = Pn(1/x)/Qn(1/x) hence: I1(x)*exp(-x) = Pn(1/x)/Qm(1/x)/sqrt(x)

Generated by Wolfram Mathematica:

<<FunctionApproximations`
ClearAll["Global`*"]
f[x_]:=Sqrt[x] Exp[-x] BesselI[1,x]
g[z_]:=f[1/z]
{err,approx}=MiniMaxApproximation[g[z],{z,{2^-33,1/7.75},9,8},WorkingPrecision->60]
poly=Numerator[approx][[1]];
coeffs=CoefficientList[poly,z];
TableForm[Table[Row[{"'",NumberForm[coeffs[[i+1]],{50,50},ExponentFunction->(Null&)],"',"}],{i,0,Length[coeffs]-1}]]
poly=Denominator[approx][[1]];
coeffs=CoefficientList[poly,z];
TableForm[Table[Row[{"'",NumberForm[coeffs[[i+1]],{50,50},ExponentFunction->(Null&)],"',"}],{i,0,Length[coeffs]-1}]]