# calculate pi

• March 3rd, 2013, 01:43 AM
begii
calculate pi
hi everyone I feel so stupid asking help for these.
i NEED HELP with these part of my code my prompt said :
(computing Π (PI) ) You can approximate (PI) value by using the following
series:
Π = 4( 1  1/3 + 1/5  1/7 + 1/9  1/11 +  - 1/(2i -1) + 1/(2i + 1)
Write a method that calculate value of π by using the above series, using
public static double pi()
assume i = 1000000

ok so I have been testing it but I really did get any far :

for ( double i = 1; i< 1000000; i+=2) {

// with these I try to increment the value of i to get to the serie.

//I did these after and test it and the output is all wrong and I know it

sum = (1/((2*i)+1));

sum = sum + (1/((2*i)-1));

sum ++;

double pi = 4*(sum);

// I know is wrong I but I canīt figure it out what to do.

I am a first semester student of computer science I got the beging of the semester really fast but these is getting harder and my professor is not helping that much..

if someone can help me pleaseee!
• March 3rd, 2013, 06:02 AM
2kaud
Re: calculate pi
Possibly its the maths that you need some help with. The general term in the series you are using is 1/(2 * n - 1) where n starts at 1 and continues in increments of 1 until its terminating value - in your case 1000000. So when n = 1, the term is 1/(2 * 1 - 1) which is 1/1, n = 2 the term is 1/(2 * 2 - 1) which is 1/3 etc. Every even term is negative so when n is even the term is subtracted from the sum rather than added. The result is then four times the sum.

How a go with this info and post back your code if you still have problems. Please use [code] tags when posting code to make it readable (click go advanced, highlight the code and then click '#'). As it's homwork I can't really give you the code but I'll comment on anything you post back.
• March 3rd, 2013, 01:43 PM
begii
Re: calculate pi
thankss

so I got these so far,
but I donīt know how to get the total value of the sum, and also if I should update the variable sum ?

Code:

public class Pi{
public static void main(String[] args)
{

sum =0;

for (int i=3 ; i< 1000000; i+=2){

if (sum%2==0){

sum = 1/(2 * i - 1);
}
else {

sum =  1/(2 * i + 1);

}

}

• March 3rd, 2013, 01:50 PM
2kaud
Re: calculate pi
That's not c++. That looks like java or c#? This is the c++ forum.
• March 3rd, 2013, 02:00 PM
begii
Re: calculate pi
I know but I couldnīt find out a C# forum can u still give me feedback?
• March 3rd, 2013, 02:19 PM
2kaud
Re: calculate pi
On the main forum page the c# forum is called c-sharp programming under the header .net programming. You need to scroll down the page until you find it. I really suggest you re-post there for c# related questions.

However, the help I can give is this. You loop needs to start at 1 until 1000000 and go up in increments of 1. For every value of the loop you need to calculate the individual term using 1 / (2 * i - 1). Then once you have calculated the term, add it to the sum if i is odd or subtract it from the sum if i is even.
• March 3rd, 2013, 03:54 PM
begii
Re: calculate pi
thankss! I appreciate the help