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# How to solve multiple equations dependent on each other?

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R7 DR on 30 Jan 2015
Answered: Niels on 30 Jan 2015
Hi
How to code this situation?
I have two equations, which are dependent on each other. Y=2X+5----(1) and X=2Y+5-----(2) The initial value of X=1, then I have to solve these equation repeatedly for 10 times.
Thanks

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### Accepted Answer

Niels on 30 Jan 2015
Since you depend on your previous answers, you can simply loop through the equations and store the answers.
x = ones(1,10); % also contains your initial x
y = ones(1,10); % just to preallocate y as well
for i=1:9 % loop 9 times
y(i) = 2*x(i) + 5; % calculate the y-value
x(i+1) = 2*y(i) + 5; % calculate the 'next' x-value
end
y(10) = 2*x(10) + 5; % finish off by calculating the final y-value
If you only care about the final value, this suffices:
x = 1;
for i=1:9
y = 2*x + 5; % calculate the y-value
x = 2*y + 5; % calculate the 'next' x-value
end
y = 2*x + 5;

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