To express SOS1 variables using binary variables in MATLAB, you can use the following steps:
1. Create binary variables for each of the original variables in your SOS1 set. For example, if your SOS1 set has variables x1, x2, x3, then you would create binary variables y1, y2, y3.
2. Add the following constraints to your model:
a. For each pair of binary variables yi and yj, add the constraint yi + yj <= 1. This ensures that at most one binary variable can take the value of 1.
b. For each original variable xi and its corresponding binary variable yi, add the constraint xi <= yi. This ensures that if the binary variable is set to 0, then the original variable must also be 0.
c. For each pair of adjacent variables in the SOS1 set, xi and xj, and their corresponding binary variables, yi and yj, add the constraint yi + yj >= xj. This ensures that if xj is non-zero, then at least one of the corresponding binary variables must also be non-zero.
3. Add your objective function and any additional constraints to your model as needed.
4. Solve the model using a solver such as MATLAB's built-in linprog function or an external solver.
Here is an example code snippet that demonstrates how to express SOS1 variables using binary variables in MATLAB:
```
% Define original variables
x = [5; 2; 3; 1];
% Create binary variables
y = binvar(4,1);
% Add constraints
constraints = [y(1) + y(2) + y(3) + y(4) == 1];
for i = 1:4
constraints = [constraints, y(i) <= x(i)];
end
for i = 1:3
constraints = [constraints, y(i) + y(i+1) >= x(i+1)];
end
for i = 1:4
for j = 1:4
if i ~= j
constraints = [constraints, y(i) + y(j) <= 1];
end
end
end
% Define objective function
f = [1; 1; 1; 1];
% Solve the model
[x_opt, fval] = linprog(f, [], [], constraints, [], zeros(4,1));
```
In this example, we have a set of four original variables (x1, x2, x3, x4) and we create binary variables (y1, y2, y3, y4) for each of them. We then add the constraints described above and define an objective function. Finally, we solve the model using the linprog function in MATLAB.