Need help creating a loop

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shanon
shanon 2011-10-19
Have to create a function with a loop that formulates pi using Leibniz's formula. It has to ask the user for a positive integer n&then calculate pi to n terms (terms being 4=1 , 4/3= 2, 4/5= 3, 4/7= 4, etc..)
Leibniz's formula says that pi= 4-4/3 +4/5 - 4/7 + 4/9 - 4/11 ....
OR
pi/4= 1 - 1/3 +1 /5 - 1/7 + 1/9 - 1/11...
so far, i thought to put:
function pi= pleibniz (n)
for i= 1:n pi/4=
but then i don't know what to do! please help!

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采纳的回答

Daniel Shub
Daniel Shub 2011-10-19
I wouldn't use a loop to do this (and I love loops).
  1. How could you make z equal the sequence 1, 3, 5, 7, ..., N?
  2. How could you make y equal to 4 times the reciprocal of z?
  3. How could you make x equal to the sum of the "odd" terms of y (i.e., 4/1, 4/5, 4/9, ...) and w equal to the sum of the "even terms of y (i.e., 4/3, 4/7, ...)?
  4. How can you make v equal to the sum of x and u equal to the sum of w?
  5. How can you make t be the difference between v and u?
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shanon
shanon 2011-10-19
Saw it, sorry, Wayne King, writing it out for myself, so I can see it
n= 0:13;x= ((-1).^n)./(2*n+1);
%approximate pi/4
sum(x)
x1= 4.*x;
%approximate pi
sum(x1)
I don't understand why n is 0:13 though?
@Daniel, thanks for trying to make my life more difficult.... The lab is much more complex than this, all I want is a little help on one thing. You have to go, and ask me five questions? Not what I was looking for.
Daniel Shub
Daniel Shub 2011-10-19
The problem with using a loop for this question is it doesn't really teach you that much about MATLAB. In fact, I would argue that following the steps that I laid out will teach you a lot more about MATLAB than the loop solution.
If you cannot look at Steven's solution and see that it works without running it, you really haven't solved the problem and the homework is only going to get harder.

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更多回答（2 个）

Thomas
Thomas 2011-10-19
Steven
Steven 2011-10-19
clear all; clc;
eps = 50; % precision
piOn4 = 1;
for i = 1:eps
piOn4 = piOn4 + (-1)^(i)*(1/(2*i+1))
end
piOn4
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Jan
Jan 2011-10-19
About the useless "clear all", see: http://www.mathworks.com/matlabcentral/answers/16484-good-programming-practice#answer_22301
Daniel Shub
Daniel Shub 2011-10-19
Don't overwrite i!!!!!

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