hi every one. i'm trying to plot yd in my code in terms of t but i got this error : conversion to double from sym is impossible, pls help me as soon as possible, thanx

    f11=tf([0 2.59],[62 1]);f12=tf([0 0 1.11],[1426 85 1]);
f21=tf([0 0 1.88],[2700 120 1]); f22=tf([0 2.82],[90 1]);
F=[f11 f12;f21 f22];
[G_Sym,DL,NL,~,~,DR,NR,~,~]=MFD_Form(F);
t=500:500:2000;
z1=(2.7350e-04)-((2.0022e-04)*gammainc(3.8,((t-500)/150),'upper'));
z2=(2.4202e-011)-((1.0180e-011)*gammainc(4,((t-500)/150),'upper'));
Zd=[z1;z2];
yd=NR*Zd;%%%yd is sym from mfd_form function
plot(t,yd);