Tracking a square wave with an analytical function

I have created a square wave (voltage schedule) in Excel, that I want to "track" with an analytical function.

The idea is to simulate a DC motor that has step changes in voltage.

R = 2;
L = 1e-3;
Ca = 1e-5;

% Continuous time voltage sched
Volt_vec = xlsread('voltage schedule.xlsx','C:C');

% Initial current
I_L_0 = 0;

% Initial voltage
V_C_0 = 0;

V_In = Volt_vec;

t = 0:.0001:.01;

alpha = R/2/L;  
omega_0=sqrt(1/L/Ca);   
zeta=alpha/omega_0;     
omega_d=omega_0*sqrt(1-zeta^2); 

          A=[1,        0;
             -alpha, omega_d]; % 

          b=[V_C_0-V_In;
              I_L_0/Ca];

          x=A\b;
   V = exp(-alpha*t).*(x(1)*cos(omega_d*t)+x(2)*sin(omega_d*t))+V_In;

The voltage vector is similar to:

t = 0 to .001, V = 85

t = .001 to .004, V = 30

t = .004 to .01, V = 65 etc.

Just a square wave with varying lengths of the step.

Right now I just read in the voltage vector and use it as the step input (V_In), and it doesn't work due to matrix dimensions issues.

I need the final value (t,v) before the next step jump in voltage to serve as the initial conditions for the following case.