Error using plot Conversion to double from sym is not possible

Rb=2*10^9;

syms t;

T=1/Rb;

BT=[0.25,0.3,0.4,0.5,0.6,0.7];

for ii=1:length(BT)

a=sqrt(2)*pi*BT(ii)/(T*sqrt(log(2)));

b=pi*BT(ii)/sqrt(2*log(2));

firstterm=(b/a)*(erf(a*t-b)+erf(a*t+b));

secondterm=t*(erfc(a*t-b)-erfc(a*t+b));

thirdterm=(exp(-(a*t+b).^2)-exp(-(a*t-b).^2))/(a*sqrt(pi));

phase=(pi/(2*T))*(firstterm+secondterm+thirdterm)+(pi/2);

f=-10^10:40*10^7:10^10; %-10^10:4*10^7:10^10

%**** Integration ***

p(ii,:)=int(exp(-1i*((2*pi*f*t)-phase)),t,-T,T);

q(ii,:)=int(exp(-1i*((2*pi*f*t)+phase)),t,-T,T);

sum(ii,:)=0.5*(p(ii,:)+q(ii,:));

magnitude(ii,:)=abs(sum(ii,:)); % find absolute value of complex value

sd(ii,:)=(magnitude(ii,:).^2)/T^2;

end

mn=10*log10(sd);

figure

plot(f,mn,'.-');