Many series are used to calculate the value of pi. In this blog, we compare two series, one by Gregory and another by Ramanujan.

Here is a MATLAB program that does the comparison for you. The MATLAB program can be downloaded as a **Mfile ** (better to download it, as single quotes from the web-post do not translate correctly with the MATLAB editor). The **html** file showing the mfile and the command window output is also available.

%% COMPARING TWO SERIES FOR VALUE OF PI

% Language : Matlab 2007a

% Authors : Autar Kaw

% Last Revised : October 30, 2008

% Abstract: This program compares results for the value of

% pi using a) Gregory series and b) Ramanajun series

clc

clear all

clf

format long

disp(‘This program compares results for the value of’)

disp(‘pi using a) Gregory series and b) Ramanajun series’)

disp(‘ ‘)

disp(‘Gregory series’)

disp(‘pi=sum over k from 0 to inf of (4*((-1)^k/(2*k+1))’)

disp(‘ ‘)

disp(‘Ramanajun Series’)

disp(‘1/pi=sum over k from 0 to infinity of 2*sqrt(2)/9801*((4k)!*(1103+26390k)/(k!)^4*396^(4*k))’)

%% INPUTS.

%If you want to experiment this the only parameter

% you should and can change.

% Maximum number of terms

n=30;

%% PROGRAM

%% GREGORY SERIES

pi_gregory=0;

for i=1:1:n

pi_gregory=pi_gregory+(-1)^(i+1)*4*(1/(2*i-1));

pi_gregory_array(i)=pi_gregory;

end

%% RAMANUJAN SERIES

pi_ram=0;

for i=0:1:n-1

pi_ram=pi_ram+2*sqrt(2)/9801.0*(factorial(4*i))*(1103.0+26390.0*i)/((factorial(i)^4)*(396)^(4*i));

pi_ram_array(i+1)=1/pi_ram;

end

%% THE OUTPUT

disp(‘ ‘)

fprintf(‘\nNumber of Terms = %g’,n)

fprintf(‘\nGregory Series Value = %g’,pi_gregory)

fprintf(‘\nRamanujan Series Value = %g’,1/pi_ram)

disp( ‘ ‘)

%% PLOTTING THE TWO SERIES AS A FUNCTION OF TERMS

x=1:1:n;

hold on

xlabel(‘Number of terms’)

ylabel(‘Value of pi’)

title(‘Comparing Gregory and Ramanujan series’)

plot(x,pi_gregory_array,’color’,’blue’,’LineWidth’,2)

hold on

plot(x,pi_ram_array,’color’,’black’,’LineWidth’,2)

legend(‘Gregory Series’,’Ramanajun Series’,1)

This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu.

An abridged (for low cost) book on *Numerical Methods with Applications* will be in print (includes problem sets, TOC, index) on December 10, 2008 and available at lulu storefront.

Subscribe to the blog via a reader or email to stay updated with this blog. **Let the information follow you**.

### Like this:

Like Loading...

## Author: Autar Kaw

Autar Kaw (http://autarkaw.com) is a Professor of Mechanical Engineering at the University of South Florida. He has been at USF since 1987, the same year in which he received his Ph. D. in Engineering Mechanics from Clemson University. He is a recipient of the 2012 U.S. Professor of the Year Award. With major funding from NSF, he is the principal and managing contributor in developing the multiple award-winning online open courseware for an undergraduate course in Numerical Methods. The OpenCourseWare (nm.MathForCollege.com) annually receives 1,000,000+ page views, 1,000,000+ views of the YouTube audiovisual lectures, and 150,000+ page views at the NumericalMethodsGuy blog. His current research interests include engineering education research methods, adaptive learning, open courseware, massive open online courses, flipped classrooms, and learning strategies. He has written four textbooks and 80 refereed technical papers, and his opinion editorials have appeared in the St. Petersburg Times and Tampa Tribune.
View all posts by Autar Kaw

The above iterative schemes show that the pi number can be generated by simple way using computer. But I believe the calculation of the pi number will be more easy when a simple analytical formulation of the magic number is available.

LikeLike

Can you examplize analytical formula what you mean sir?

LikeLike

Can you examplize analytical of the pi formula what you mean sir?

LikeLike

I do not know what Rohedi meant by analytical formula for pi. I have requested him to explain.

LikeLike

Oh thanks, you are pleased me to give brief explanation about the simple analytical formulation for pi number.

We know that until now there are so many formulas for pi number. The simpliest exact formula of pi is 4*arctan(1), where arctan(1)=1-1/3+1/5-1/7+1/9… But as discussed here, the primary drawback of the infinite series of 1-1/3+1/5-1/7+1/9…called as Gregory-Leibniz Series is too slowly to converg, that also shown on this link :

http://www.eveandersson.com/pi/gregory-leibniz

Actually, there is another exact formula or the pi number called Machin’s Formula

pi=16*arctan(1/5)-4*arctan(1/239)

(Please search it via google). But, there is still problem because the formula contains the arctan function.

Recently, creating the pi number until more than million digits has been performed using BBP Formula based on haxadecimal coding , please visit to this link for detail explanation,

http://en.wikipedia.org/wiki/Bailey-Borwein-Plouffe_formula

But, as explained at this link :

http://mathworld.wolfram.com/PiFormulas.html

the BBP formula was created by complicated function, and also we can’t use the formula easily.

Apologise, as I posted on http://eqworld.ipmnet.ru/forum/viewtopic.php?f=2&t=34&start=30, after a week from the last Pi Day (3/14/09) I found a simple analytic exact formula for pi number that now in preparing to be published. By using my formula, the pi number can be created by hand easily. I hope Professor Autar Kaw can inform me appropriate math journal to publish my exact pi formula.

Best Regards.

Rohedi.

LikeLike

Oh thanks, you are please me to give brief explanation about the simple analytical formulation for pi number.

We know that until now there are so many formulas for pi number. The simpliest exact formula of pi is 4*arctan(1), where arctan(1)=1-1/3+1/5-1/7+1/9… But as discussed here, the primary drawback of the infinite series of 1-1/3+1/5-1/7+1/9…called as Gregory-Leibniz Series is too slowly to converg, that also shown on this link :

http://www.eveandersson.com/pi/gregory-leibniz

Actually, there is another exact formula or the pi number called Machin’s Formula

pi=16*arctan(1/5)-4*arctan(1/239)

(Please search it via google). But, there is still problem because the formula contains the arctan function.

Recently, creating the pi number until more than million digits has been performed using BBP Formula based on haxadecimal coding , please visit to this link for detail explanation,

http://en.wikipedia.org/wiki/Bailey-Borwein-Plouffe_formula

But, as explained at this link :

http://mathworld.wolfram.com/PiFormulas.html

the BBP formula was created by complicated function, and also we can’t use the formula easily.

Apologise, as I post on http://eqworld.ipmnet.ru/forum/viewtopic.php?f=2&t=34&start=30, after a week from the last Pi Day (3/14/09) I found a simple analytic exact formula for pi number that now in preparing to be published. By using my formula, the pi number can be created by hand easily. I hope Professor Autar Kaw can inform me appropriate math journal to publish my exact pi formula.

Best Regards.

Rohedi.

LikeLike

Thanks for the post. The Mathematics magazine of MAA is a suitable journal.

LikeLike

Dear Prof.Autar Kaw,

Now, I am visiting again special to inform all visitors here that on the following link:

http://eqworld.ipmnet.ru/forum/viewtopic.php?f=2&t=157,

there are the post of exact value of Pi number in Golden Ratio expression.

Thanks for your attention,

Best Regards,

Rohedi.

LikeLike

Dear Prof.Autar Kaw,

Now, Rohedi gives special comment for the fact that 0.999… = 1 as appear at the list of automatically generated, that recently it has discussed at so many math blogs, such as at

http://ardoris.wordpress.com/2009/03/29/0999-1/

and

http://math152.wordpress.com/2009/01/13/interesting-proof-by-contradiction/.

They generally prove the above equality by using geometric series and proof by contradiction.

But, Rohedi still doesn’t believe to the existence of

0.999…=1,

because ….

Let add the both sides with pi/4,

0.999… + pi/4= 1 + pi/4,

Taking tangent function for both sides

tan(0.999… + pi/4)= tan(1 + pi/4),

we will find

[tan(.999…)+1]/[1-tan(.999…)]= [tan(1)+1]/

[1-tan(1)].

Of course mathematicians has not a reason to say that

tan(.999…)=tan(1)

How about you??

Best Regards,

Rohedi (http://rohedi.com)

LikeLike

I often visit to eqworld.ipmnet.ru, the link for pi exact formula posted by Rohedi. But recently when visiting again the website gives message “no input file specified”. I need to copy contain of the post to be learned more. How I can find the article of pi formula and some related topics?

LikeLike

Please clarify what you are looking for.

LikeLike

Yes, I met this website of numerical method guys when searching “pi number”, that was displayed by google at the third pages. And at the leave comment of this article I read some informations about Rohedi’s version of new pi exact formula. But, unfortunately, his posts has been deleted from the website of eqworld.ipmnet.ru/forum/ . Okay I try to contact Rohedi via contact us of his website rohedi.com, and I promise to back here gives further information from him. Thx Dr.Kaw.

LikeLike

Yes, I met this website of numerical method guys when searching “pi number”, that was displayed by google at the third pages. And at the leave comment of this article I read some informations about Rohedi’s version of new pi exact formula. But, unfortunately, his posts has been deleted from the website of eqworld.ipmnet.ru/forum/ . Okay I try to contact Rohedi via contact us of his website rohedi.com, and I promise to back here for giving further information from him. Thx Dr.Kaw.

LikeLike