Error "Unable to resolve the name gurobi.Model."

Answered

Abdelmalek Metidji

August 02, 2023 13:57

• 
• 

Hello,

I'm using Gurobi to solve the problem of min-cost flow on graphs with radiality contraints. Here is the code that I'm using :

n = 4;
R = [1];

% Define the isconnected function
isconnected = @(G) numel(unique(conncomp(G))) == 1;

% Set the connectivity ratio of the graph
p = 1;

% Generate a random adjacency matrix
AA = triu(rand(n) < p, 1);
AA = AA + AA';

% Create a connected graph from the adjacency matrix
while ~isconnected(graph(AA))
    AA = triu(rand(n) < p, 1);
    AA = AA + AA';
end
S = AA;

for i = 1:n
    for j = 1:n
        if ismember(i, R) == 1
            S(n, i) = 1;
            S(i, n) = 1;
        else
            S(n, i) = 0;
            S(i, n) = 0;
        end
    end
end
G = graph(S);
p=plot(G);


% Define other problem data (cost vector c, constraint rho, etc.)
% (Replace these with the actual data)
c = ones(n, n); % Cost vector c (n x n matrix)
for i=1:n-1
     rho_in(i)=0;
end

rho_in(n)=n-1-length(R);


for i=1:n-1
    if ismember(i,R)==0
    rho_fin(i)=1;
    else
        rho_fin(i)=0;
    end
        
    %input(sprintf('rho_fin(%d)=',i));
end
rho_fin(n)=0;
RHO=(rho_in-rho_fin)';

  
try
    % Create Gurobi model
    model = gurobi.Model();

    % Add variables b_{i,j} and x_{i,j}
    b = model.addVars(n, n, 'B'); % Binary variables
    x = model.addVars(n, n, 'C'); % Continuous variables

    % Set objective function
    obj = 0;
    for i = 1:n
        for j = 1:n
            if S(i, j) == 1
                obj = obj + c(i, j) * b(i, j) * x(i, j);
            end
        end
    end
    model.setObjective(obj, 'minimize');

    % Add constraints
    % Constraint: \sum_{j\in N(i)} b_{i,j}x_{i,j} - \sum_{j\in N(i)} b_{j,i}x_{j,i} = \rho(i) for all i
    for i = 1:n
        expr = 0;
        for j = 1:n
            if S(i, j) == 1
                expr = expr + b(i, j) * x(i, j) - b(j, i) * x(j, i);
            end
        end
        model.addConstr(expr == RHO(i));
    end

    % Additional Radiality Constraints
    for j = 1:n
        if ~ismember(j, R) % If j is not in the set R (set of sources)
            model.addConstr(sum(b(:, j)) == 1);
        end
        for i = 1:n
            if S(i, j) == 1
                model.addConstr(b(i, j) + b(j, i) <= 1);
            end
            if ismember(j, R) % If j is in the set R (set of sources)
                model.addConstr(b(i, j) == 0);
            end
        end
    end

    % Optimize the model
    model.optimize();

    % Display the solution
    disp('Objective value:');
    disp(model.objval);
    disp('Binary variables b:');
    disp(model.getAttr('x', b));
    disp('Continuous variables x:');
    disp(model.getAttr('x', x));

catch gurobiError
    disp('Error reported by Gurobi');
    disp(gurobiError.message);
end

I get always this error message: Error reported by Gurobi
Unable to resolve the name gurobi.Model.

I want to know please what is exactly the probleml?. Thank you.

Related to

• MATLAB

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 13, 2026 01:39

  This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  David Torres Sanchez

  • Gurobi Staff

  August 02, 2023 15:43

  Hi,

  This does not look like the MATLAB API, please check some of the simple examples e.g. mip1.m and revise your code.

  Cheers, 
  David

  0

Post is closed for comments.