How to find the correct range of tow?

i have created a code for maximum throughput sensing time optimization with duration tow but I need to find the tow which varies from (0,1) . I cant find the incrementation which is done by the system

The graph i obtained is

the graph which I expected

and the program which i used is

clc 
close all
PH0=0.4
Pa=10;
y=0.1;
N=3;
yi=[1,2,4];
Pdbar=0.8;
tow=0:0.2:1     %the tow i used
Pi=[2,4,3];
alpha=sqrt((2*y)+1)*qfuncinv(Pdbar);
xy=0    
    for i =2:N
    x=1+((Pi(i)*yi(i))/((1+sum(Pi(i)*yi(3:N)))));
    xy=xy+log2(x);
    end
d=sum(Pi(2:N)*yi(1))
f=sum(Pi(2:N).*yi(2:N))   
beta=xy-(d/(1+f))    
fs=100000;
z=1+sum(Pi(2:N).*yi(2:N));
S=(Pa*yi(1))/z;
x1=1-qfunc(alpha+y*sqrt(tow*fs))
y1=log2(1+(tow*S/(1-tow))+beta)
c=x1*y1    
R_tow=PH0*(1-tow).*c+beta;
disp(R_tow)
plot(tow,R_tow)
ylim([1,1.7])

the tow value should be find ,should i need to use the optimization toolbox?

How the obtain the smoothened graph?