Why is my plot empty?

%%% Solves HW #6 Q2 %%%

% ------ Defining Variables ------ %
y0 = 0;
v0 = 0;
m = 60;
k = round(mean([6,6,0,1]*1000));
b = k/20;
g = 9.81;
Wn = sqrt(k/m);
Xst = (m*g)/k;
L = (b*Wn)/2*k;
tt = linspace(0,5,101);

%%% ------ Closed Form Solution ------ %%%
%%%% BROKEN %%%%

T = tt.*Wn;
A = -Xst;
B = (L*pi*A)/(sqrt(1-L^2));
closed = @(t) exp(-L*pi*t) .* (A*cos(sqrt(1-L^2)*t) + ...
    B*sin(sqrt(1-L^2)*t)) + Xst;

subplot(2,2,1)
plot(tt,closed(tt),'-')
title('Closed Form Solution')
xlabel('Time (s)')
ylabel('X(t) (cm)')

Answer 1

[DGM]

The plot doesn't display because all of the output values (except for tt = 0) are NaN.

L is a relatively large number ~2E6, so for nonzero time values:

exp(-L*pi*t) % this is zero
A*cos(sqrt(1-L^2)*t) % this is -Inf
B*sin(sqrt(1-L^2)*t) % this is -Inf

so 0*Inf = NaN