How do I connect data points with a line?

Question

Byeongchan Min 2020-4-25

0
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回答： Pravin Jagtap 2020-4-28

Hi

I made a quadratic iteration using 'for'. Below is my code;

a=2.95; x11=0.65; x12=-0.001;
for i=0:50;
    y11=f(a,x11); 
    y12=f(a,x12); 
    i=i+1;
    figure(1)
    subplot(2,2,1)
    title('alpha=2.95')
    hold on 
    plot(i,y11,'-.')
    hold on
    plot(i,y12,'-d')
    axis([0 50 -1 1])
    x11=y11; x12=y12;
end
function f=f(a,x); 
  f=a*x*(1-x); 
end

So I wanted to add a line connecting points (i,y11) and (i,y12) respectively.

Especially for points (i,y12), because it diverses to negative infinity too fast and I wanna show its divergeance only, instead of showing like all the way down to 10^-13 of y axis.

Hompage says to assign a linestyle using such like '-o' or '-.', but none of those gave me a line but only dots.

What should I do to get lines?!

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dpb 2020-4-25

You're only plotting a point a at time...save the computed points and then plot the arrays after the loop has calculated all the data is probably easiest...or save the previous and plot the new from the previous to the new point before overwriting it (the current) in the loop...

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Answer 1

Pravin Jagtap 2020-4-28

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Hello Byeongchan,

It is not clear that what you want to achieve from your code. Especially, increment of iterator 'i' inside the for loop and the use 'subplot' is not clear. I am assuming that you want to plot a function y= f(x) and connect two points on that curve. Please refer to the following code and check whether you want to achieve the same:

% Inputs
a=2.95; x11=0.65; x12=-0.001;
% Generating X and Y 
X = -1:0.01:1;  % It can be chagened as per requirements 
Y = 2.95.*X.*(1-X);
% Calculating function values at x11 and x12
y11=funVal(a,x11); 
y12=funVal(a,x12); 
% Generating data for line 
XX = [x11 x12];
YY = [y11 y12];
% Plotting
plot(X,Y);
hold on;
plot(XX,YY,'-o');
% Function defination
function f=funVal(a,x)
  f=a*x*(1-x); 
end