Two options for the plot, depending on what you want to do:
Plot in the loop:
figure
hold all
for alpha=0:0.2:2*pi
p=(p_m*sqrt(1-c^2))/(1-c*cos(alpha-delta));
plot (alpha,p, 'p')
end
hold off
plot (alpha,p, 'p')
xlabel('\alpha')
ylabel('p')
Plot after the loop:
alpha=0:0.2:2*pi;
for k = 1:numel(alpha)
p(k) = (p_m*sqrt(1-c^2))/(1-c*cos(alpha(k)-delta));
end
figure
plot (alpha,p, '-p')
xlabel('\alpha')
ylabel('p')
Make appropriate changes to get the result you want.
Before the plot loop (everything up to and including the ‘delta’ assignment), your code is unchanged.