MATLAB: If statement

if

hey guys I'm trying to do an if statement inside an embedded matlab function in simulink, but it is not working, I don't know why.
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This is the matlab function 
function [Wv_membr,lambda_m] = fcn(Ist,T_st,phi_ca,phi_an)
Mv=18.02E-3;
n=381;
Afc=280;
F=96485;
tm=0.01275;
%phi_an=0.5;
%phi_ca=0.80;
am=(phi_ca+phi_an)/2;
if (am>0) && (am<=1)
  lambda_m=0.043+17.81*am-39.85*am^2+36*am^3;
elseif (am>1) && (am<3)
  lambda_m=14+1.4*(am-1);
end
i=Ist/Afc;
if (lambda_m<2)
  Dy=1E-6;
elseif (lambda_m>=2) && (lambda_m<=3)
  Dy=1E-6*(1+2*(lambda_m-2));
elseif (lambda_m>3) && (lambda_m<4.5)
  Dy=1E-6*(3-1.67*(lambda_m-3));
elseif (lambda_m>=4.5)
  Dy=1.25E-6;
end
if (phi_an>0) && (phi_an<=1)
  lambda_an=0.043+17.81*phi_an-39.85*phi_an^2+36*phi_an^3;
elseif (phi_an>1) && (phi_an<3)
  lambda_an=14+1.4*(phi_an-1);
end
if (phi_ca>0) && (phi_ca<=1)
  lambda_ca=0.043+17.81*phi_ca-39.85*phi_ca^2+36*phi_ca^3;
elseif (phi_ca>1) && (phi_ca<3)
  lambda_ca=14+1.4*(phi_ca-1);
end
pm_dry=0.002;
Mm_dry=1.1;
cv_an=pm_dry/Mm_dry * lambda_an;
cv_ca=pm_dry/Mm_dry * lambda_ca;
Dw=Dy*exp(2416*(1/303-1/T_st));
nd=0.0029*lambda_m^2+0.05*lambda_m-3.4E-19;
Nv_membr=nd*i/F * Dw*(cv_ca-cv_an)/tm;
Wv_membr=Nv_membr*Mv*Afc*n;
end
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when I run it, it says that lamda_m is not a defined variable, but this is impossible. It is very weird to me. I wonder for some help.

Best Answer

When I uncomment the lines as you mentioned, I still do not get an error:
phi_an=0.5;
phi_ca=0.80;
am=(phi_ca+phi_an)/2;
if (am>0) && (am<=1)
  lambda_m=0.043+17.81*am-39.85*am^2+36*am^3;
elseif (am>1) && (am<3)
  lambda_m=14+1.4*(am-1);
end
if (lambda_m<2)
  Dy=1E-6;
elseif (lambda_m>=2) && (lambda_m<=3)
  Dy=1E-6*(1+2*(lambda_m-2));
elseif (lambda_m>3) && (lambda_m<4.5)
  Dy=1E-6*(3-1.67*(lambda_m-3));
elseif (lambda_m>=4.5)
  Dy=1.25E-6;
end
All is fine.
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