MATLAB: For loop for fibonacci series

for loop

i am supposed to write a fibonacci series that calculate up to n term and (n-1) term but i am stuck at calculating the (n-1)term. can anyone help? ( i am new to matlab)

a = 0;
b = 1;
x = n-1;
n = input('Enter number of term desired');
for i = 1:n %term for n
    
    fprintf('\t')
    fprintf('%d',a);
    c = a + b;
    a = b;
    b = c;
end
for i = n:x %term for n-1
    
    fprintf('\t')
    fprintf('%d',a);
    c = a + b;
    a = b;
    b = c;
    
end

Best Answer

In case of series, it is better to store each value. Please see below code that generatesa fibonacci sequence, and stores all the values in the variable"a";

a(1) = 0;
a(2) = 1;
n = input('Enter number of term desired ');
for i = 3:n
   a(i) = a(i-1)+a(i-2);
end

From here, if you want the n'th term, you do a(n), if you want the n-1, then you do a(n-1).

You method of trying to find the n-1 term can work with the following modification;

a = 0;
b = 1;
n = input('Enter number of term desired');
for i = 1:n-2 %term for n
    c = a + b;
    a = b;
    b = c;
end
a_n  = c; % nth term
a_n1 = a; %(n-1) term

Related Solutions

MATLAB: N th Fibonacci number with function

function [c] = fibo (a, b, n)
n = input('n:');

Every time your user calls your fibo function, you're going to ask them to pass a value into it for n (as the third input) then immediately turn around and prompt them to type in a replacement value for n.

IMO if part of your design requires your user to enter data manually, you should have (at least) two separate functions: the interface function that can call input and then just calls the processing function and the processing function that operates solely on data passed into it (no prompting of the user allowed.)

But that's a bit of an aside. You already have most of what you want. It's not too difficult to translate your first script into a function.

n = input('n:');

Turn this first statement into the function declaration line. "function theOutputs = fibonacci(theInputs)". I'll let you decide what to write in place of theOutputs and theInputs.

fibo = zeros(1,n);
for n = 1:n

Reusing the variable name technically works, but it can be confusing that the role of n kind of changes. I'd use a different variable name for the loop variable.

    if n==1
        fibo(n)=0;
    else
        if n==2
            fibo(n)=1;
        else
    fibo(n)=fibo(n-1)+fibo(n-2);
        end
    end
end
disp(fibo);

Turn this last line into the line that defines whatever variables you need to return. It should assign into whatever variables appear in theOutputs above.

MATLAB: Fibonacci series, while loop

Well, what is important to me is you have made a credible effort, and gotten close. In fact, you did compute Fibonacci sequence elements.

First, you should have preallocated the vector a, which would make MATLAB more efficient.

What would i change in the code you show?

N = 16; % how far out
a = zeros(1,N); % preallocation
a(1) = 1;
a(2) = 1;
for n = 3:N % a for loop is simpler to write than a while loop
  a(n) = a(n-1)+a(n-2);
end

But how about that ratio thing? You cannot use the limit function to compute a limit as you did. Sorry. But the limit is just the ratio of two consecutive numbers from that sequence. So now, you want to see how well those ratios approach the expected limit as N grows larger.

ratio = zeros(1,N-1);
for n = 1:N-1
   ratio(n) = a(n)/a(n+1);
end
format long g
ratio'
ans =
                         1
                         2
                       1.5
          1.66666666666667
                       1.6
                     1.625
          1.61538461538462
          1.61904761904762
          1.61764705882353
          1.61818181818182
          1.61797752808989
          1.61805555555556
          1.61802575107296
          1.61803713527851
          1.61803278688525

What is the expected limit supposed to be? It is approaching that theoretical limit?

Best Answer

Related Solutions

MATLAB: N th Fibonacci number with function

MATLAB: Fibonacci series, while loop

Related Question