Why some output show 0-by-1

I am confused about some output has numerical answer, but some show empty system. I did use the same function and the input are similar.

ro = 5;

q = 1.6*10^(-19)

Si_emin = 68.5

Si_emax = 1414

Si_eref = 9.2*10^16

Si_ea = 0.711

Si_n = dp(ro,q,Si_emin,Si_emax,Si_eref,Si_ea)

ro = 5;

q = 1.6*10^(-19)

Si_hmin = 44.9

Si_hmax = 470.5

Si_href = 2.23*10^17

Si_ha = 0.719

Si_p = dp(ro,q,Si_hmin,Si_hmax,Si_href,Si_ha)

ro = 5;

q = 1.6*10^(-19)

GaAs_emin = 500

GaAs_emax = 9400

GaAs_eref = 6*10^16

GaAs_ea = 0.394

GaAs_n = dp(ro,q,GaAs_emin,GaAs_emax,GaAs_eref,GaAs_ea)

ro = 5;

q = 1.6*10^(-19)

GaAs_hmin = 20

GaAs_hmax = 491.5

GaAs_href = 1.48*10^17

GaAs_ha = 0.38

GaAs_p = dp(ro,q,GaAs_hmin,GaAs_hmax,GaAs_href,GaAs_ha)

ro = 5;

q = 1.6*10^(-19)

InP_emin = 0

InP_emax = 5000

InP_eref = 4*10^17

InP_ea = 0.45

InP_n = dp(ro,q,InP_emin,InP_emax,InP_eref,InP_ea)

ro = 5;

q = 1.6*10^(-19)

InP_hmin = 10

InP_hmax = 170

InP_href = 4.87*10^18

InP_ha = 0.62

InP_p = dp(ro,q,InP_hmin,InP_hmax,InP_href,InP_ha)

function x = dp(ro,q,min,max,ref,a)

syms x

eqn = 1/(ro*q*(min+(max-min)/(1+(x/ref)^a)))-x == 0

x = vpasolve(eqn,x)

end

Output：

q = 1.6000e-19

Si_emin = 68.5000

Si_emax = 1414

Si_eref = 9.2000e+16

Si_ea = 0.7110

eqn =

x =

915687197686292.77386563464132068

Si_n =

915687197686292.77386563464132068

q = 1.6000e-19

Si_hmin = 44.9000

Si_hmax = 470.5000

Si_href = 2.2300e+17

Si_ha = 0.7190

eqn =

x =

2758477083642648.6175367991525707

Si_p =

2758477083642648.6175367991525707

q = 1.6000e-19

GaAs_emin = 500

GaAs_emax = 9400

GaAs_eref = 6.0000e+16

GaAs_ea = 0.3940

eqn =

x =

Empty sym: 0-by-1

GaAs_n =

Empty sym: 0-by-1

q = 1.6000e-19

GaAs_hmin = 20

GaAs_hmax = 491.5000

GaAs_href = 1.4800e+17

GaAs_ha = 0.3800

eqn =

x =

Empty sym: 0-by-1

GaAs_p =

Empty sym: 0-by-1

q = 1.6000e-19

InP_emin = 0

InP_emax = 5000

InP_eref = 4.0000e+17

InP_ea = 0.4500

eqn =

x =

Empty sym: 0-by-1

InP_n =

Empty sym: 0-by-1

q = 1.6000e-19

InP_hmin = 10

InP_hmax = 170

InP_href = 4.8700e+18

InP_ha = 0.6200

eqn =

x =

7477430144904512.3068191021258371

InP_p =

7477430144904512.3068191021258371

Answer 1

[Thorsten]

It seems that vpasolve cannot solve the equation with the given input to it returns an empty symbol.