non-integer passed to boolean operator

[yi lu]

I have written the following script for a function. Each step is correct and I've checked the function itself is also correct. However, when I went to the final step, plot. it shows error.

gnuplot> a(x)=91.25e-21*x

gnuplot> b(x)=0.8125/x

gnuplot> T1(x)=(sin((1-a(x))*b(x)))**2/((1-a(x))**2)

gnuplot> T2(x)=(N*0.927*sin(b(x))*sin(a(x)*b(x))*sin((1-a(x))*b(x)))/(a(x)*(1-a(x)))

gnuplot> T3(x)=(S*0.927*cos(b(x))*sin(a(x)*b(x))*sin((1-a(x))*b(x)))/(a(x)*(1-a(x)))

gnuplot> T4(x)=0.5*0.86*(sin(a(x)*b(x)))**2/((a(x))^2)

gnuplot> Y(x)=(0.08*T1(x)-d*0.2828*T2(x)+d*0.2828*T3(x)+(d**2)*T4(x))

gnuplot> plot N=0, S=0, Y(x);plot N=0, S=1, Y(x)

         non-integer passed to boolean operator