stem-plot difference of equations

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Tony
Tony on 16 Dec 2013
Commented: Walter Roberson on 31 Dec 2013
Here is the question
Find numerically and stem-plot the solutions of the difference equations [1<=k<=10]
a. y(k+1) - 3*k*y(k) = 0
b. y(y+1) - k*y(k) = 1
assume that y(1)=1
not sure if i am looking at this properly but here is what i was thinking. a and b do not have the same y values after 1 since in order to get 0 for the first one y(2) needs to be 3 while for equation b y(2) needs to be 2. So solve them differently and then plot? i am not sure which would be my x and y for stem plot as well. This looks simple but its confusing me not sure if am over thinking.
Thank you for your time
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Tony
Tony on 16 Dec 2013
that is the main question sorry if it was not but i am not sure if its suppose to be answered separate or together
Walter Roberson
Walter Roberson on 24 Dec 2013
Are you sure that (b) should have y(y+1) on the left side, and not y(k+1) ??

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Accepted Answer

Walter Roberson
Walter Roberson on 16 Dec 2013
Once you have the set of values x1 with y1, and x2 with y2, you can use interp1() to interpolate each set of data over a common set of times; then you can stem().
For example,
y1_interp = interp1(x1, y1, 1:10)
y2_interp = interp1(x2, y2, 1:10)
plot(1:10, y1_interp, 1:10, y2_interp)
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Tony
Tony on 31 Dec 2013
Edited: Tony on 31 Dec 2013
edit actually doesn't seem to display properly with stem
second edit - its good thank you happy holiday
Walter Roberson
Walter Roberson on 31 Dec 2013
At the command line give the command
format long g

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More Answers (1)

Youssef Khmou
Youssef Khmou on 24 Dec 2013
Tony, try this iterative method :
y1=zeros(10,1);
y2=zeros(10,1);
y1(1)=1;y2(1)=1; % initial conditions
for t=1:9
y1(t+1)=3*t*y1(t);
y2(t+1)=1+t*y2(t);
end
k=1:10;
figure, stem(k,y1), hold on,stem(k,y2,'r')

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