How to get a line plot without markers, on a logarithmic scale in a for loop?

I want to express my reuslts from a for loop on a logaritmic scale (on x-axis). However, I am having trouble in getting both the logarithmic displays and line plots in one go.

1. With the semilogx: display in logarithmic scale is achieved but only if I identify a marker such as 'o' or 's'. However, I can't get it to plot show the results as a line or a line plot.
2. With the addpoints approach: Sure, I get a line plot. Still, in this case I am unable to solve the other problem of displaying on a logarithmic scale.

To keep the script brief, I am leaving out the constants I used. You can put in random values for execution. This is my for loop:

t=1:10000;
for i=1:numel(t)
  f2=(v293/v)^(10*(alpha^4));
  f1=1+((1-alpha)^2)*log(350/Blaine);
  n=nzero*f1*f2;
  etaalpha=exp(-n*alpha);
  Aalpha=k*(A/((k*alphau)+alpha))*(alphau-alpha);
  alpha=Aalpha*etaalpha*exp(-EA/(R*T))*exp(EA/(R*293))+alpha;

  semilogx(i,alpha,'o-');                     % outputs a logarithmic x-axis with markers (sadly not a line)
  hold on
  % hold all

  % addpoints(h,t(i),alpha(1))               % outputs a line plot
  % drawnow limitrate 
end

[Scott MacKenzie]

Why are you leaving out the constants? Your code can't execute if it accesses unitialized variables.

[dpb]

  semilogx(i,alpha,'o-'); 

You told it to NOT use a line but only a marker.

See the doc for linestyle triplets for the details.

[Mansoor Aziz]

I have tried using the 'o-' syntax but still it shows only markers; no line.

Answer 1

[Scott MacKenzie]

As noted clearly by @dpb, you need to not use the 'o-' syntax to get the lines without markers:

i = 1:10;
alpha = rand(1,10);

tiledlayout('flow');
nexttile;
semilogx(i,alpha,'o-'); % your code: line+maker
nexttile;
semilogx(i,alpha); % line only (i.e., no marker)

[Mansoor Aziz]

I'm sorry for appearing so needy here but I'm new to MATLAB and the problem persists.

Your solutions are based on vectorized code where both the variables have the same number of elements.

I think the problem lies somewhere in the implementation of the for loop. On the one hand, I have a vector 't' that has 100 pre-allocated elements, and on the other hand, a variable 'alpha' containing a single element that changes its value on every iteration. I intend to plot this 100 element vector and the single element ever-changing variable.

[Scott MacKenzie]

Hmm, I think we're getting close. Try

semilogx(alpha); 

instead of

semilogx(i, alpha); 

Seems you trying to plot alpha as a vector against i as a scalar. That's a no-no and is likely why you aren't seeing the lines. There aren't any lines to plot!

But, the x-argument in semilogx is not needed. So, try the first example above, with just alpha, and let's see what happens.

BTW, my first comment lamented that you did not provide code that could be executed. When you post questions in the future, it would help if you posted all the code, or a sufficient subset of the code that can be executed.

[Mansoor Aziz]

Scott, I tried doing that as well: Still No luck!

And why do you suggest, the 'x' argument must be left out? How will it know what to plot it against?

I didn't provide all of the code for the purpose of keeping the query (or the area thereof) short. Its an ugly mess. But you are right; one must provide atleast an executable portion of the code. Find the code file attached in all its haphazard and jumbly glory.

Thankyou for your cooperation.

[Scott MacKenzie]

If the x-values are omitted, they are assumed. So, for example, if you have 10 y-values (10 alpha-values, in your case), then the values along the x-axis automatically become 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[Mansoor Aziz]

I just ended up initiating and filling up another vector. That vector was plotted against time outside the for-loop.

for i=1:numel(t)
.
.
.
alpha=Aalpha*etaalpha*exp(-EA/(R*T))*exp(EA/(R*293))+alpha;
Aplot(end+1)=alpha;
end
semilogx(t,Aplot)

[Scott MacKenzie]

Yes, that should work, provided t and Aplot are vectors of the same length. You can also just use

semilogx(Aplot)

as noted in my previous comment.

BTW, here is the documentation on the use of semilogx when ommitting the 1st argument, X: