# Error while plotting the polar plot

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CHANDRABHAN Singh on 22 Sep 2021
Commented: CHANDRABHAN Singh on 22 Sep 2021
%I have an expression which is plotted using the polarplot.
a = 1/(2.*cos(theta))
e = 0.5;
thet = -60:1:60;
theta = thet .*(pi/180);
c = cos(theta);
p = 4*(1-e^2).*(c.^2) + (2*e - 1)^2;
q = 2*(1-e*e).*c + (2e-1)*sqrt(4*(1-e*e).*(c.^2) + 5 *e*e - 4*e);
r = q./p;
polarplot(theta,r);
hold on;
%Now if i solve the expresion for e=0.5 analytically and then try plotting the expression a = 1./(2.*cos(theta));
polarplot(theta,a);
hold off; %Why the graphs are not same while both the expressions are same.

Chunru on 22 Sep 2021
e = 0.5;
thet = -60:1:60;
theta = thet .*(pi/180);
c = cos(theta);
p = 4*(1-e^2).*(c.^2) + (2*e - 1)^2;
% q = 2*(1-e*e).*c + (2e-1)*sqrt(4*(1-e*e).*(c.^2) + 5 *e*e - 4*e);
% 2e-1 is the number 2x10^(-1), rather than 2*e-1 !!!
q = 2*(1-e*e).*c + (2*e-1)*sqrt(4*(1-e*e).*(c.^2) + 5 *e*e - 4*e);
r = q./p;
polarplot(theta,r);
hold on;
a = 1./(2.*cos(theta));
polarplot(theta,a);
hold off; CHANDRABHAN Singh on 22 Sep 2021
Thanks.

R2020b

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