# .Modelica_LinearSystems2.StateSpace.'-'.subtract

## Information

#### Syntax

```ss = StateSpace.'-'.subtract(ss1, ss2)
```

#### Description

This operator function computes the subtraction of two state space systems connected in parallel, i.e. the inputs are the same and the outputs of the two systems are subtracted. Therefore, the systems must have the same number of inputs and outputs but not the same number of states. The resulting system has an order of system_order1 + system_order2.

The operator is used by writing just the following command:

```ss3 := ss1 - ss2;
```

#### Example

```  StateSpace ss1 = StateSpace(A=[-1, 0; 0, -2], B=[1; 2], C=[0, 1], D=);
StateSpace ss2 = StateSpace(A=[-3, 0; 0, -4], B=[3; 4], C=[0, 2], D=);

StateSpace ss3;

algorithm
ss3 := ss1 - ss2;
// ss.A = [-1, 0, 0, 0; 0, -2, 0, 0; 0, 0, -3, 0; 0, 0, 0, -4],
// ss.B = [1; 2; 3; 4],
// ss.C = [0, 1, 0, -2],

// ss.D = ,
```

#### Interface

```function subtract
import Modelica;
import Modelica_LinearSystems2.StateSpace;
input StateSpace ss1 "State-space system 1";
input StateSpace ss2 "State-space system 2 is subtracted from system 1";
output StateSpace result(redeclare Real A[size(ss1.A, 1) + size(ss2.A, 1), size(ss1.A, 2) + size(ss2.A, 2)], redeclare Real B[size(ss1.B, 1) + size(ss2.B, 1), size(ss1.B, 2)], redeclare Real C[size(ss1.C, 1), size(ss1.C, 2) + size(ss2.C, 2)], redeclare Real D[size(ss1.D, 1), size(ss1.D, 2)]) "= ss1 - ss2";
end subtract;
```

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