My while loop is giving an error "Array indices must be positive integers or logical values." I'm trying to calculate the golden ratio within epsilon 0.001.

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Alan Clemenson 2018-4-8

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评论： Alan Clemenson 2018-4-8

I am stuck in the initiation of my while loop. I attached the file and an image of the code. I've done everything I can think of but I'm still learning and can't see what I'm doing wrong here.

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David Fletcher 2018-4-8

编辑：David Fletcher 2018-4-8

There are a couple of issues that I can immediately see:

You've set k=0 and are indexing x(k), x(k-1), and x(k-2) in your while loop. In Matlab, array indices start at 1 so all of these indexing operations are invalid. You've also set N=3:k - since k=0 this equates to 3:0 which is an empty array since your end value is less than your start value and you haven't set a negative step value.

Alan Clemenson 2018-4-8

Thank you, I thought I could make k count until false and that final k value would fill that space in N. Is there a way I can do that?

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Answer 1

David Fletcher 2018-4-8

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Probably something more like this:

%Program Description:
%This program takes 2 numerical inputs and calculates/estimates the golden
%ratio within epsilon 0.001.
%
% Record of Revisions:
%     Date         Programmer          Description of change
%     ====         ==========          =====================
%    4/7/18      Alan Clemenson          Original Code
%   
%User Prompts
n1=input('type in value for first #:  ');
n2=input('type in value for second #:  ');
% Compute results
%index for the numbers following n1&n2 in the fibonacci sequence 'x'.
%Previous fib no.
x(1) = n2-n1
% Place Assignment of n1&n2 in the sequence
x(2)= n1
x(3)= n2
%the absolute value of the difference between two ratios>0.001
    while (abs(x(3)/x(2)-x(2)/x(1))>0.001);
        %The Fibonacci sequence.
        nextFib=x(2)+x(3);
        x=circshift(x,-1);
        x(3)=nextFib;
        Ratio=x(3)/x(2);
      end
  fprintf('\n The Golden Ratio = %f \n',Ratio);