Is it possible to manually connect the ABCD matrices to obtain the ss representation

I know that the ss of the ABC and D matrices can be obtained by using the comman ss, but it is possible to do it manually through connect, i tried to do this:

clc;
clear all;

k = 1;
m = 1;
b = 1;


A = [0 1; -k/m -b/m];
B = [0 1/m]';
C = [1 0];
D = [0];

a = tf(A);
a.u = 'x';
a.y = 'dxa';

b = tf(B);
b.u = 'uc';
b.y = 'dxb';

Sum1 = sumblk('dx = dxa + dxb');

c = tf(C);
c.u = 'x';
c.y = 'yc';

d = tf(D);
d.u = 'uc';
d.y = 'yd';

Sum2 = sumblk('y = yc + yd');

integrator = inv(tf('s'));  
integrator.u = 'dx';
integrator.y = 'x';

T = connect(a,b,c,d,Sum1,Sum2,integrator,'uc','y');

Its block diagram is the common SS blocks interconection but I added my signals for reference:

but I get this warning message:

Warning: The following block inputs are not used: dxa,dxb,x(1),x(2).

> In DynamicSystem/connect (line 265)

In interconectando (line 45)

Warning: The following block outputs are not used: dxa(1),dxa(2),dxb(1),dxb(2),x.

> In DynamicSystem/connect (line 270)

In interconectando (line 45)

What could i be doing wrong? because the T system is empty, therefore the interconnection was wrong.

Answer 1

[Paul]

Need to modify two lines of code as follows:

clc;
clear all;
k = 1;
m = 1;
b = 1;
A = [0 1; -k/m -b/m];
B = [0 1/m]';
C = [1 0];
D = [0];
a = tf(A);
a.u = 'x';
a.y = 'dxa';
b = tf(B);
b.u = 'uc';
b.y = 'dxb';
Sum1 = sumblk('dx = dxa + dxb',2);  % need the second argument for vector signals.
c = tf(C);
c.u = 'x';
c.y = 'yc';
d = tf(D);
d.u = 'uc';
d.y = 'yd';
Sum2 = sumblk('y = yc + yd');
integrator = eye(2)/tf('s');  % two integrators for two states
integrator.u = 'dx';
integrator.y = 'x';
T = connect(a,b,c,d,Sum1,Sum2,integrator,'uc','y');