Question

matlab help

Answer 1

%% Problem 9.8
%{
One interesting preoperty of a Fibonacci sequence is that the ratio of the
values of adjacent members of the sequence aproaches a number valled "the
golden ratio" or (phi). Create a program that accepts the first two
additonal values in the sequence as user input and then calculates
additional values in the sequence until the ratio of adjacent values
converges to within 0.001. You can do this in a while loop by comparing the
ratio of element k to element k - 1 and the ratio of element k - 1 to
element k - 2. If you call your sequence x, then the code for the while
statement is

while abs(x(k)/x(k-1)-x(k-1)/x(k-2))>0.001
%}

Answer 2

@jim_thompson5910

Answer 3

how much do you have written?

Answer 4

nothing. I didn't really know where to start. Let me work on it for a bit. I made a mini program before on the Fib sequence.

Answer 5

`Let me work on it for a bit`
alright, take your time

Answer 6

@jim_thompson5910 I don't undertand what it is asking

Answer 7

ok so the first thing I'd do is write the code where you get your inputs

these inputs will help set up the fibonacci sequence

Answer 8

`Create a program that accepts the first two additonal values in the sequence as user input`

Answer 9

N = input('Enter first value: ');

fib = zeros(1, N);
fib(1) = 1;
fib(2) = 2;
k = 3;

while k <= N
fib(k) = fib(k-1) + fib(k-2);
k = k + 1;
end

fprintf('The Fibonacci sequence to %d terms is \n', N);
fprintf('%0.f', fib);
fprintf('\n');

Answer 10

ok that code looks like it will work

Answer 11

But this is for a single input

Answer 12

btw you don't have to have `fib = zeros(1, N);`

at least I think you don't

Answer 13

am I heading in the right direction here?

Answer 14

% asking user to input any number
N1 = input('Enter first value: ');
N2 = input('Enter second value: ');

fib(1) = N1;
fib(2) = N2;
k = 3;

fib(k) = fib(k-1) + fib(k-2);
while abs(fib(k)/fib(k-1)-fib(k-1)/fib(k-2))>0.001
fib(k) = fib(k-1) + fib(k-2);
k = k + 1;
end
disp(fib)

Answer 15

% ask the user for the starting 2 values
% the user should type in 1, then 2.
fib(1) = input('Enter first value: ');
fib(2) = input('Enter second value: ');
% in all honesty, this shouldn't be an input section since the fib sequence doesn't change. % The starting values are always the same.


% as long as the difference between the adjacent ratios is greater
% than 0.001, keep generating terms
k = 3;
while diff > 0.001
fib(k) = fib(k-1) + fib(k-2);
diff = fib(k)/fib(k-1) - fib(k-1)/fib(k-2);
k = k + 1;
end

fprintf('The Fibonacci sequence to %d terms is \n', k);
fprintf('%0.f', fib);
fprintf('\n');

Answer 16

Reading and studying what you displayed

Answer 17

I like what you posted better.

Answer 18

You should find that `fib(k)/fib(k-1)` will approach the golden ratio phi (as k approaches infinity)

https://www.mathsisfun.com/numbers/golden-ratio.html

http://prntscr.com/b6xji4

Answer 19

actually I see why the teacher wants an input section. The only problem is that the right inputs must be typed in or else it won't work.


For instance,
input1 = 1
input2 = 2
or
input1 = 5
input2 = 8
are valid input combos


but
input1 = 5
input2 = 10
is invalid

Answer 20

ignore the comment where I wrote `% the user should type in 1, then 2. `
you can start at any point in the fib sequence as long as you type in numbers that belong to the sequence and those numbers are adjacent (second input being larger)

Answer 21

so fib(1) and fib(2) won't work since I need to assign an input() func to them because fib(1) = 1 and fib(2) = 2 won't work

Answer 22

^That means I would have to enter value 1 or 2

Answer 23

when you type in `fib(1) = 1` it says there's an error?

Answer 24

I have not tested. I was fixing my code

Answer 25

but you said `because fib(1) = 1 and fib(2) = 2 won't work`

Answer 26

It was more of a question. if you assign fib(1) and fib(2) I thought this doesn't allow the user to input values beyond 2

Answer 27

you can add another input line if you need more inputs

Answer 28

true or I could just do this

% asking user to input any number
N1 = input('Enter first value: ');
N2 = input('Enter second value: ');

fib(1) = N1;
fib(2) = N2;
k = 3;

Answer 29

yes that works too. It seems a bit wasteful though because N1 isn't used for anything else. So why not just take out the middleman and connect the two sections directly?

Answer 30

so go like this

fib(1) = input('...
fib(2) = input('....

Answer 31

your way isn't wrong, it just takes up more lines than needed

Answer 32

yes you can write it like that

Answer 33

so what does the 1 and 2 represent? Induces or the program knowing you put a value in for the first prompt and second prompt?

Answer 34

you mean fib(1) what the 1 represents?

Answer 35

yeah

Answer 36

fib(1) represents the first value in the fib vector
fib(2) represents the second value in the fib vector

you do not need to create a blank fib vector because you can add on values by simply writing the next bit of code


this bit of code

fib(k) = fib(k-1)+fib(k-2)

will sets up the kth term based on the previous two terms. Again we don't need to set up a blank vector. This allows the fib vector to get as big as we need (as long as the memory can hold it of course)

Answer 37

Oh okay

Answer 38

% asking user to input any number
fib(1) = input('Enter first value: ');
fib(2) = input('Enter second value: ');
k = 3;

while diff > 0.001
fib(k) = fib(k-1) + fib(k-2);
diff = fib(k)/fib(k-1) - fib(k-1)/fib(k-2);
k = k + 1;
end
fprintf('The Fibonacci sequence to %d terms is \n', k);
fprintf('%0.f', fib);
fprintf('\n');

Answer 39

it gives me an error


Enter first value: 1
Enter second value: 2
Error using diff
Not enough input arguments.

Answer 40

hmm let me think

Answer 41

this is what my matlab says

Error: "diff" previously appeared to be used as a function or command, conflicting with its use here as the name of a variable.
A possible cause of this error is that you forgot to initialize the
variable, or you have initialized it implicitly using load or eval.

Answer 42

why did we remove the abs() function? Don't we need it?

Answer 43

hmm I messed up and forgot about the abs

Answer 44

yes we need it

Answer 45

okay

Answer 46

Putting the abs() I still get an error
Enter first value: 1
Enter second value: 2
Error using diff
Not enough input arguments.

Answer 47

ok I got it to work

Answer 48

here is the m file and the command output as two separate files

Answer 49

I changed each instance of `diff` to `difference`. Apparently Matlab has a function named `diff` for differentiation


I also changed the line
`fprintf('%0.f', fib);`
to
`fprintf('%0.f, ', fib);`
I added in a comma and a space to make the formatting much cleaner

Answer 50

why did we have to assign diff = 10?

Answer 51

The fib sequence Matlab spits out is
1, 2, 3, 5, 8, 13, 21, 34, 55, 89

Take the ratios of the terms
89/55 = 1.61818181818181
55/34 = 1.61764705882352

then subtract
1.61818181818181 - 1.61764705882352 = 0.0005347593583

So we're within range

Answer 52

`why did we have to assign diff = 10?`

when Matlab first sees the "difference" variable in the line
while difference > 0.001
it has no idea what the value of "difference" is. So I just made up some number larger than 0.001

This is to set up the variable and define it to be some value. The value of "difference" is then recomputed to be some smaller decimal number

Answer 53

Okay makes sense. Thank you very much.

Answer 54

No problem.

I'm not sure if it's me, but I have a feeling your copy of Matlab can handle "diff" just fine? and you don't have to change it to "difference" ?

Answer 55

I was actually going to just leave it or at least try to run it with diff instead of difference.

Answer 56

see if matlab throws an error if you have "diff"

Answer 57

Oh that is neat when you change %0.f to %0.f, it puts commas between each number

Answer 58

Okay it runs just fine now. I made diff = 5;

Answer 59

ok great

Answer 60

the only down side of putting comma after the f is that a commas appears after 89

Answer 61

it shows ....89,

Answer 62

It doesn't matter I will just leave it. It bothers me though.

Answer 63

yeah true. I'm not sure how to get rid of that pesky comma

Answer 64

No worries, I will just leave it.