trouble plotting curved line

I'm trying to plot a curved line but it keeps coming out linear. I was told it could be because I linspaced both the T and S variables but I changed the S vectors and it still comes out linear. The for loop produces the correct values I need so I'm not sure where I'm going wrong. Any help would be appreciated

T4=833.15;
Tmax=1407;
st1=1.661;
T2ac=603;
st2ac=2.4143;
S2ac=6.193;
st3=3.368;
S3ac=7.8666;
st_23=st2ac:.001:st3;
for i=1:length(st_23)
    DDD(i)=st_23(i)-st2ac+S2ac;
end
t_2_3=linspace(T2ac,Tmax,length(DDD));
plot(DDD,t_2_3)

Answer 1

[Kevin Holly]

I'm not sure what you are trying to graph. I don't know what the T and S variable are suppose to be. Here is a guess of what I think you could be looking for:

T4=833.15;
Tmax=1407;
st1=1.661;
T2ac=603;
st2ac=2.4143;
S2ac=6.193;
st3=3.368;
S3ac=7.8666;
st_23=st2ac:.001:st3;

DDD(1:length(st_23))=st_23(1:length(st_23))-st2ac+S2ac;
t_2_3=linspace(T2ac,Tmax,length(DDD));
semilogx(t_2_3,DDD)