Need help with error on 'neighbors' function

Hi everyone,

I have a model developed in simulink with network connections. Each time the model has to analyse its neighbor nodes to progress. It is working fine during initial few seconds (upto 1000 sec), and I am facing error on 'neighbors' function after that (total runtime - 8760 sec). Each node have 2 neighbors.

s = [1 1 2 2 3 3 4 4]';
t = [2 3 1 4 1 4 2 3]';
v = [n1;n2;n3;n4]';

g = graph (s,t);
node = numel (v);
neg = find(v<0);
values_neg = v(neg);
ele = numel(neg);
z = zeros(1,node);
for k = 1:ele
    for i = 1:node
        if v(1,i)<0
            a = neighbors(g, i);
            b = v(a);
            s = 0;
            for j=1:connection
               if b(j)>0
                   s = s+b(j);
               end
            end
            z(1,i) = s+v(1,i);
        else
            z (1,i)= 0;
        end
    end
    z';
    zmin = min (z);
    imin = find(z==zmin);
    n = neighbors(g, imin);
    vmin = v(imin);
    [vmax, imax] = max(v(n));
    borrowvalue = min(-vmin, vmax);
    v(imin) = v(imin) + borrowvalue;
    v(n(imax)) = v(n(imax)) - borrowvalue;
end

Error as follows:

Node ID must be a positive integer scalar not greater than the number of nodes in the graph (4). Error in 'four_Node/Subsystem/Energy management' (line 55) n = neighbors(g, imin);

Component: Simulink | Category: Model error

An error occurred while running the simulation and the simulation was terminated

Caused by:

• Simulation stopped because of a runtime error.

I am using MATLAB 2021a. I hope some expericed member in the community can help me with this.

[Chunru]

You need a more complete code snippet to explain variables such as v, z, and zmin. Better still, provide an executable code segments to demonstrate the error.

[Shemin Sagaria]

s = [1 1 2 2 3 3 4 4]';
t = [2 3 1 4 1 4 2 3]';
v = [n1;n2;n3;n4]';
node = numel (v);
neg = find(v<0);
values_neg = v(neg);
ele = numel(neg);
z = zeros(1,node);

for k = 1:ele
    for i = 1:node
        if v(1,i)<0
            a = neighbors(g, i);
            b = v(a);
            s = 0;
            for j=1:connection
               if b(j)>0
                   s = s+b(j);
               end
            end

            z(1,i) = s+v(1,i);
        else
            z (1,i)= 0;
        end
    end
    z';
    zmin = min (z);
    imin = find(z==zmin);
    n = neighbors(g, imin);
    vmin = v(imin);
    [vmax, imax] = max(v(n));
    borrowvalue = min(-vmin, vmax);
    v(imin) = v(imin) + borrowvalue;
    v(n(imax)) = v(n(imax)) - borrowvalue;
end

[Shemin Sagaria]

It runs for a few time steps without any problems and then the error is popping up.

[Christine Tobler]

The error message is because the second input to neighbors is larger than the number of nodes in graph g. How is the graph g constructed? Does this change between time steps?

Possibly you need to make sure to use the constructor graph(s, t, numNodes) so that you have the correct number of nodes even if node 4 isn't connected to any edge.

[Shemin Sagaria]

Thank you. I will try this