How to create a loop calcualtion?

Question

Kokalz 2012-7-19

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评论： NUR ZAFIRAH MOHD SIDEK 2017-6-20

Hi Guys! I am writing a GUI that processes some excel data and got to a point, where I need it to do some loop calculation. However, I have absolutely no idea how to do it. I tried going through all Doug's tutorials, but could not find anything, that would explain it. So here's the idea:

Say i need a 1x20 matrix. I know the first value of this vector, but all he other values come from the calculations that require the first value. So here's the sequence of the calculation:

Take the first value > input it into formulas with other variables > get the second value > use the second value to get the 3 rd value > get the 3rd value > use the 3rd value to get the 4th value > and so on.... Then plot all the acquired values on the graph against time.

Could someone help me out with it? Tell me if I made i too confusing..

Thank you, guys!

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NUR ZAFIRAH MOHD SIDEK 2017-6-20

Hi guys, can some one help me to solve my problem?

i've be facing difficulty to find the number of function evaluation. let's say that i have f(x)=x^3+x^2-2 with initial value of x(0)=1.5

i want to calculate x(n+1)=x(n)-(f(x(n)/fprime(x(n))) until n=5

thus, i want to calculate how many time of f(x(n)) have been use until n=5. but if the first iteration has use f(x(1)) then the second iteration also use f(x(1)), it is considered as we only use f(x(1)) one time only.

can someone help me

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Answer 1

Thomas 2012-7-19

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Probably something like this..

num_values=10;    % total values
first_val=2;    
output=zeros(1,num_values);  %preallocate space for output
output(1)=first_val;    % first value of output
for count=2:num_values
output(count)=output(count-1)+25; %formula current value depends on previous
end
output
plot(output)

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Answer 2

Ryan 2012-7-19

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So you have a 1 x 20 vector you want to fill off of knowing just the first value and each previously value determines the next? Is this what you're looking for:

t = 1:1:20; % for graphing later
x = zeros(1,20);
x(1) = .5; % Assign first value of "x"
for m = 2:numel(x)
  x(m) = sin(x(m-1)); % Calculates the current cell "m" off of prior cell "m-1"
end
figure,plot(t,x)

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Answer 3

C.J. Harris 2012-7-19

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Here is an example of a quick loop that calculates a value based on the previous value. The loop simply calculates the value as twice the previous value:

A = zeros(1,20); % Initialize array
A(1) = 1;        % Set first value to 1
for nLoop = 2:length(A)        % Start loop at second value
   A(nLoop) = A(nLoop-1) * 2;  % Answer is twice the previous value
end