Change from continuous model to discrete model

This is my code describe continuous system

%Parameter Massa
m1 = 8095; % massa train set 1 dalam kg
m2 = 8500; % massa train set 2 dalam kg
g  = 10;

%Parameter Gaya
f1 = 205.10^3; % dalam N
f2 = 302.10^3; % dalam N

c_0_1 = 0.01176;
c_1_1 = 0.00077616;
c_2_1 = 4.48 ;

c_0_2 = 0.01176 ;
c_1_2 = 0.00077616;
c_2_2 = 4.48;

v_0 = 300;

hstar = 120;

a_1   = -1./m1.*(c_1_1 + 2.*c_2_1.*v_0);  
a_2   = -1./m2.*(c_1_2 + 2.*c_2_2.*v_0); 

a_1_head = 1-(a_1.*hstar);
a_2_head = 1-(a_2.*hstar);
b = 1;

p_1 = -1./m1.*(c_0_1 - c_2_1.*(v_0).^2);
p_2 = -1./m2.*(c_0_2 - c_2_2.*(v_0).^2);

A = [0  a_1_head      0        0;
     0     0          0        0;
     0 (a_2_head - 1) 0 a_2_head;
     0      0         0        0
     ];
 
B = [-b.*hstar         0;
      b                0;
      0        -b.*hstar;
     -b                b
     ];
 
U_t = [f1; f2;];

C = [1 0 0 0;
     0 1 0 0;
     0 0 1 0;
     0 0 0 1;];
 
W = [((a_1 - 1).*v_0) - (p_1.*hstar);
     0;
     ((a_2 - 1).*v_0) - (p_2.*hstar);
     ((a_1 - 1).*v_0) - (p_1.*hstar);
     ];
 

W in my continuous system i assume as D

i want to change to discrete use this code

first i find the ss_model

 ss_model = ss(double(A),double(B),C,W);
 

But there is an error

 Error using ss (line 345)
The values of the "b" and "d" properties must be matrices with the same number of columns.

Error in AREtrial2 (line 66)
ss_model = ss(double(A),double(B),C,W);

The plan after i get the ss_model i use c2d to convert to discrete model

d_sys = c2d(ss_model,0.1);

But before i use c2d i need help about the error

and is that right my methode to change from continuous model to discrete model