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)

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