I can't write recursive function in Matlab (Please help me)

I tried many times but couldn't write a recursive function in Matlab. I don't know how to do it. My friends, I would be glad if someone could help me.

[Rooter Boy]

I wrote simply code blog, i want to recursive function of it. I want to like this: function [itr] = newton(x,tol)

[Rik]

Do you explicitly want a recursive function, or do you just want to implement this algorithm?

[Rooter Boy]

User will enter values of x and tol. I will call function. After i will enter x and tol. Simply, i will enter f(x) and tolerance. These are my inputs. My output is number of iteration. If iteration < tolerance, take output. For example, i called function newton(x,tol). after, i entered values randomly. such as newton(1.8,0.01). My output will be 3. Because 3.iterations is < tolerance. To sum up, I already sent my code blog of newton raphson, so you can see above. I need recursive function of this.

[Rooter Boy]

How can I do it? If someone is help me, i will be very happy.

[Rik]

At the very least you will have to start your newton.m file with the line

function itr=newton(x,tol)

Then the rest of you code can calculate the number of iterations needed. It doesn't sound like you need a recursive function. The loop you have there should work.

[Rooter Boy]

Sir, I need recursive function. For example, i have a question like this. I should call recursive function.

You know recursive function should contain your function. You do not use while loop.

[Rik]

I don't speak the language in this screenshot, but I don't see any indication that the only way to solve this is recursion. I see no indication that a while loop wouldn't work. You're free to implement it any way you like. What is your question?

[Rooter Boy]

I'm a master student in computer engineering. This is my homework. I agree with you. But i need do with recursive function.

[Rik]

Then implement it as a recursive function. What is your question?

[Rooter Boy]

function [itr] = newton(x,tol) how can we apply this according to the above question. Maybe we can use ifelse instead while.

function [itr] = newton(x,tol)

x=0;

tol=0;

if hata>tol.......

I don't know how to adapt it.

[Rik]

Just because you aren't getting the help you were hoping for dosn't make this question not appropriate, so I removed your flag.

[Stephen23]

https://web.archive.org/web/20201024174625/https://www.mathworks.com/matlabcentral/answers/624223-i-can-t-write-recursive-function-in-matlab-please-help-me

Answer 1

[Rik]

In case you just want to know how to create a recursive function at all:

function n=I_call_myself(n)
disp(n)
if n>0
    n=I_call_myself(n-1);
else
    disp('n has reached 0')
end
end

[Rooter Boy]

Sir, I know principles of recursive function. How do we define my function? I don't understand it.

[Rik]

I have no clue how you should force this algorithm in a recursive function that makes any sense. This seems the perfect place for a while loop. The point is that in a recursive function you have the function call itself. At some point that recursion should stop, in your can when hata<tol.

[Rooter Boy]

I tried write but result is false. output should be 3 for solution. I don't know how to call. Firstly i define function but i can't.

function [itr] = newton(x,tol)

hata=tol+1;
n=1;
itr=0;
if hata>tol
      x(n+1)=0.2*(4*x(n)+(32/power(x(n),4)));
      hata=abs(x(n+1)-x(n));
      n=n+1;
      itr=itr+1;
disp('itr');
end

[Rik]

You need to use while instead of if. For readability I would also suggest you include the closing end for you function.

function [itr] = newton(x,tol)
hata=tol+1;
n=1;
itr=0;
while hata>tol
    x(n+1)=0.2*(4*x(n)+(32/power(x(n),4)));
    hata=abs(x(n+1)-x(n));
    n=n+1;
    itr=itr+1;
end
disp(itr);
end

If you want to make it recursive you should probably have two outputs of your function, or use the length of x to define itr and n:

%untested code:
function [itr,x] = newton(x,tol)
hata=tol+1;
n=numel(x);
itr=n-1;
x(n+1)=0.2*(4*x(n)+(32/power(x(n),4)));
hata=abs(x(n+1)-x(n));
if hata>tol
    [itr,x] = newton(x,tol);
    return
end
disp(itr);
end

[Rooter Boy]

code didn't work.

Error in newtont (line 9)

[itr,x] = newton(x,tol);

[Rik]

What was the error? You need to provide the full error message. If you don't, we can only give you this advice: change the code.

[Rooter Boy]

Sir, I found solutions myself. This is advanced level coding. I want to delete these questions. If you help me about this topic, i will be happy.

Thanks for everything by the way.

[Rik]

Sorry, once you receive an answer it is considered rude to delete it, so the system will not allow you to do that. People with a similar question might find the posts here helpful.