homework help, my loglog wont plot a line

function [] =FFAplot(a,b,k)
%UNTITLED Summary of this function goes here
%   Detailed explanation goes here
A=size(a);
B=size(b);
K=size(k);
p=(1/100);
T=100;
if A(1,1)==B(1,1)
    if A(1,2)==B(1,2)
    if (B(1,1)==K(1,1))||(B(1,2)==K(1,2))

      j=0;
      i=1:K(1,2);
             Qi=zeros((A(1,1)),(A(1,2)));
      while j==0    
      % Qi=((b(1,i))+(((a(1,i))/(k(1,i)))*(1-((-log(1-p)).^(k(1,i))))));
      loglog((10),(10^6),'r')
      hold on
      plot(T,((b(1,i))+(((a(1,i))/(k(1,i)))*(1-((-log(1-p)).^(k(1,i)))))),'r')

%loglog(((b(1,i))+(((a(1,i))/(k(1,i)))*(1-((-log(1-p)).^(k(1,i)))))),T)

      end
      end
      end
  end

end

MY code wont plot anything it keeps just giving me the graph with the x and y values but no ploted line

Answer 1

[Star Strider]

It won’t because you didn’t tell it to. You told it to plot a point, and since the default behavoiur of plot is to connect two (or more) points with lines, it drew nothing.

If you want it to plot the point, plot a marker:

loglog((10),(10^6),'pr')

[Faith Dominguez]

Is there a way to get loglog to plot a line? was looking it up on Matlab help but i cant find where it says the specifications to get a line. thank you

[Walter Roberson]

To plot a line, you need to pass a list of two or more points to one of the plotting functions.

... What you should be doing is storing the x and y coordinates that you are plotting at into a vector, and not plotting inside the loop. Plot the vectors after the loop.

I notice that your T is not changing, so your points would all be at x = 100. Is that what you wanted?

You are not changing j inside your loop, so your while j==0 is an infinite loop.

[Star Strider]

It depends on what you want to plot.

Try this:

figure
loglog([1 10], [1 100000], 'b')                     % Plot Arbitrary Function
hold on
loglog(xlim, [1; 1]*[10 10^6],'-r')                 % Plot Parallel Red Lines
hold off
axis([xlim    1  1E+7])                             % Set ‘axis’ Limits To Be Cure To Show Lines

[Faith Dominguez]

function [] =FFAplot(a,b,k)
%UNTITLED Summary of this function goes here
%   Detailed explanation goes here
A=size(a);
B=size(b);
K=size(k);
p=(1/100);
T=100;
if A(1,1)==B(1,1)
    if A(1,2)==B(1,2)
    if (B(1,1)==K(1,1))||(B(1,2)==K(1,2))
        Qi=zeros(1,K(1,2));
    for   i=1:K(1,2)
     Qi(1,i)=((b(1,i))+(((a(1,i))/(k(1,i)))*(1-((-log(1-p)).^(k(1,i))))));
    loglog((1),(10^6))
    hold on
   % plot(T,(b(1,i))+(((a(1,i))/(k(1,i)))*(1-((-log(1-p)).^(k(1,i))))),'pr')

      loglog(T,Qi,'pr')

      end
      end
  end

end

i've changed the code to this, i do want T to stay 100 , i think i have it storing the value into the array Qi

[Walter Roberson]

I would suggest, though, that if you only have a single x value, that using a loglog plot does not make sense, that semilogy would make more sense.

[Faith Dominguez]

The graph is supposed to look like this and the only way i could get x to look like that was using loglog

[Walter Roberson]

Ah.

With your T being constant you are only going to vertical lines.

Also when you use 'pr' you specify pentagram marker in red, but you would not get any line. You would need a line specification as well such as '-pr' to get lines. Which might fold back on themselves... I doubt you really want T (x coordinate) to be constant.

[Star Strider]

Also, we never did resolve the problem of ‘K(1,2)’ being anything other than 1. If it is greater than 1, then ‘i’ is a vector. That is going to cause problems.