You are plotting the data using fplot. This will give you the function, which you have used to plot when you try to extract the data from figure. If you insist to extract the data from figure (which is not necessary) you may consider using plot.
syms x
warning off
alpha = -0.1;
sigma = 0.1;
eps = -0.1;
e = 0.2;
a = 2;
lambda = 2;
M = 4;
psi_list = [10, 30, 40, 50, 5, 15, 20, 25];
figure
hold on
for i = 1:numel(psi_list)
psi = psi_list(i);
hbar = @(x) a - a.*x + x;
A1 = eps + alpha^3 + (3 * sigma^2 * alpha);
B1 = @(x) (-3 * lambda * M) * ((hbar(x).^2) + (2 .* hbar(x) .* alpha) + (sigma^2) + (alpha^2));
a1 = @(x) tanh(M .* hbar(x));
b1 = @(x) 1 - ((tanh(M .* hbar(x))).^2);
c1 = (M * alpha) - ((M^3 * A1)/3);
d1 = 2 * (M^2) * (1 + lambda);
C1 = @(x) a1(x) + (b1(x) .* c1);
D1 = @(x) d1 .* ((hbar(x).^3) + (3 .* (hbar(x).^2) .* alpha) + (3 .* hbar(x) .* (alpha)^2) + (3 .* hbar(x) .* (sigma)^2) + eps + (3 * alpha * (sigma^2)) + (alpha^3));
f1 = @(x) B1(x) + (3 * lambda .* C1(x) .* hbar(x)) + (3 * lambda .* C1(x) .* alpha) + (D1(x) .* C1(x));
f2 = @(x) 12 * (M^2) * (1 + lambda) .* C1(x);
f3 = psi * (e^3);
f4 = (1 + lambda) *180 * ((1 - e)^2); % 180 is not given in paper
f5 = 1/(2 + lambda);
F = @(x) ((f5 .* f1(x))./f2(x)) + (f3/f4);
q1 = @(x) hbar(x) ./ (2 .* F(x));
Q1 = integral(q1,0,1);
q2 = @(x) 1./(F(x));
Q2 = integral(q2,0,1);
Q = Q1/Q2;
p1 = @(x) (1./F(x)) .* ((0.5 .* hbar(x)) - Q);
P = @(x) integral(p1,0,x);
xi = linspace(0,1) ;
PP = zeros(size(xi)) ;
for j = 1:length(xi)
PP(j) = P(xi(j)) ;
end
plot(xi,PP)
end
legend(num2str(psi_list'))
ylim([0 1])
set(gca, 'ytick', 0:0.1:1);
set(gca, 'xtick', 0:0.2:1);
xlabel('x')
ylabel('P(x)')
