ploting in for loop

I wrote sum which is xs for below calculation There is something wrong with my code below that i can not figure it out?

clc
t=cputime;
k=0;
for p=1:1:7
    dt=10^-p;
k=0:1.35/dt;
xs = 2/(sqrt(pi))*sum(exp(-(k*dt).^2)*dt)
e=cputime-t;
semilogx(e,dt)
end

Answer 1

[Walter Roberson]

Try this:

k=0;
for p=1:1:7
  t=cputime;
  dt(p)=10^-p;
  k=0:1.35/dt(p);
  xs = 2/(sqrt(pi))*sum(exp(-(k*dt(p)).^2)*dt(p))
  e(p)=cputime-t;  
end
semilogx(1./dt, e)

You were plotting timestep as if it were a consequence of execution time. Also, as p increases, dt decreases, so if you plot dt then it is getting smaller and smaller and so your datapoints were getting further left, which is more difficult for people to understand. If you plot against 1./dt then you are plotting time as a consequence of number of data samples used, which is much more natural for people.

[Ahmet Oguz]

Thanks i figure it out now.

Answer 2

[Daniel kiracofe]

"there is something wrong" is pretty vague, so I'm totally guessing at what your problem is. But this seems like a reasonable guess. If this doesn't answer you question then you need to post more detail about what is your specific problem.

clc
t=cputime;
k=0;
for p=1:1:7
  dt(p)=10^-p;
  k=0:1.35/dt(p);
  xs = 2/(sqrt(pi))*sum(exp(-(k*dt(p)).^2)*dt(p))
  e(p)=cputime-t;  
end
semilogx(e,dt)

[Ahmet Oguz]

same mistake accured there is no graph

[Walter Roberson]

I would make a small change, and move the

t=cputime;

to inside the for p loop. Otherwise you are getting cumulative time since you started, instead of time for that particular refinement.