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index must be a positive integer or logical.

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sharif
sharif 2014-3-11
编辑： Chris C 2014-3-12
c1=3.29;
c2=9.90;
c3=0.77;
c4=0.20;
Ln=zeros(1,length(t));
for n=1:1:100;
for t=0:-0.1:-1;
Ln(t)=-(c1+c2*log(n)*log(-t))-(c3+c4*log(n));
semilogx(n,Ln(t));
end
end
I really want t to count negative, what am I supposed to do??
  3 个评论
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Marta Salas
Marta Salas 2014-3-11
编辑：Marta Salas 2014-3-11
You're going to define an index that it's not related with t but with the size of t. However I don't understand what you are trying to plot there. Which is the result you are expecting from that code? what do you want to plot on semilogx?
sharif
sharif 2014-3-11
It is an approximate model of flat edge in communication systems where I must have 10 different lines running from n=1 to n=100

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采纳的回答

Chris C
Chris C 2014-3-11
I'm still not reall clear on what you're looking for, but try this version of Marta's code...
c1=3.29;
c2=9.90;
c3=0.77;
c4=0.20;
t = linspace(0,-1,10); %definition of t vector
n = linspace(1,100);
Ln=zeros(length(t),length(n));
for i=1:length(t)
for j = 1:length(n);
Ln(i,j)= -(c1+c2*log(n(j))*log(-t(i)))-(c3+c4*log(n(j)));
end
semilogx(n,Ln(i,:))
hold on
end
  2 个评论
sharif
sharif 2014-3-11
yes I think this method is correct, although the graph is wrong, I have to check why it's wrong, thanks
Chris C
Chris C 2014-3-12
编辑：Chris C 2014-3-12
What's wrong about the graph? If it's because the lines are all blue all you have to do is populate the data first within the for loops and then graph it all at once after the loops instead of plotting a line after each iteration around i.

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更多回答（2 个）

dpb
dpb 2014-3-11
Keep the time as associated independent vector of same length as the solution vector but numbered from 1:N instead of trying to use it as an index.
Marta Salas
Marta Salas 2014-3-11
A solution is this:
c1=3.29;
c2=9.90;
c3=0.77;
c4=0.20;
Ln=zeros(1,length(t));
t= 0:-0.1:-1; %definition of t vector
for n=1:1:100;
for i=1:length(t);
Ln(i)= -(c1+c2*log(n)*log(-t(i)))-(c3+c4*log(n));
semilogx(n,Ln(i));
end
end
Take into account semilogx(n,Ln(i)) is plotting a point. is this the right solution?
  7 个评论
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Marta Salas
Marta Salas 2014-3-11
Sorry, I don't really understand what you mean about 10 lines.
dpb
dpb 2014-3-11
Well, read and do a little thinking on your own...fix the upper limit on the for loop to be 1:length(n)

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