running a consensus protocol on a directed graph created my an Adj-matrix

getting weired error that i dont understand

"Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 6-by-2."

the warning appers on ux(i,1) = ux(i,1) + (x(:,j)- x(:,i)); most likely it will happen for the line after that as well

close all; clear all; clc

max_iter = 600;
N = 6;                         % Number of agents
dt = 0.02;

% Agents' Initial Positions
x0 = [0, 2, 2, 4, 4, 3]';          
y0 = [0, 1,-1, 1,-1, 3]';

A = [0,1,0,0,0,0; 1,0,0,0,0,0; 1,1,0,0,1,0; 0,1,0,0,0,0; 0,0,1,1,0,0; 0,1,0,1,0,0];
G= digraph(A)
% Initialize vectors
x = zeros(N,max_iter);
y = zeros(N,max_iter);
xc = zeros(2,max_iter);
x(:,1) = x0;
y(:,1) = y0;
xc(:,1) = (1/N*ones(1,N)*[x0,y0])';

% Initialize plot
figure(1), hold on
set(gca,'xcolor','none','ycolor','none')
agenPlot = plot(x(:,1),y(:,1),'o','markersize',16,'MarkerFaceColor',[0.12,0.49,0.65],'MarkerEdgeColor','none');
xBplot = plot(xc(1,1),xc(2,1),'x','markersize',16,'MarkerFaceColor',[0.62,0.49,0.15],'linewidth',3);
axis([-1,5,-3,3])

for k = 1:max_iter-1
    
    % Initialize zero velocities
    ux = zeros(N,1);           
    uy = zeros(N,1);
    
    % FILL THIS PART
    % Compute consensus
    for i = 1:N
        inNeighbors= predecessors(G,i)
        for j = inNeighbors
            ux(i,1) = ux(i,1) + (x(:,j)- x(:,i));
            uy(i,1) = uy(i,1)+ (y(:,i)-y(:,j));
        end
    end
    
    % Integration step
    x(:,k+1) = x(:,k) + ux.*dt;
    y(:,k+1) = y(:,k) + uy.*dt;
    
    % Store centroid's position
    xc(:,k+1) = (1/N*ones(1,N)*[x(:,k),y(:,k)])';
    
    % Update plot
    set(agenPlot,'xdata',x(:,k),'ydata',y(:,k))
    set(xBplot,'xdata',xc(1,k),'ydata',xc(2,k))
    drawnow
end

figure(2), hold on
title('Solution to Q.2.c')
set(gcf,'color','white')
plot( 1:max_iter , sqrt(xc(1,:).^2 + xc(2,:).^2),'b','linewidth',2 )
plot( 1:max_iter , sqrt(x.^2 + y.^2),'k' )
legend({'$\bar{x}$','$x_i$'},'interpreter','latex','fontsize',16)
xlabel('Iterations','fontsize',16)
ylabel('$\| x \|$','interpreter','latex','fontsize',16)

Answer 1

[Matt J]

Did you mean to have this?

ux(i,1) = ux(i,1) + (x(i,j)- x(i,i))

It's not clear from your original code how you expected to get a scalar value on the right hand side.

[Tiara DeRosa]

well i change some stuff around found out that i can use indegree to get the in negbours of each node

and i use your change and got the out put of the indegree matrx

n = 6×6

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

2 4 1 2 1 0

i also got this error message "Index in position 2 is invalid. Array indices must be positive integers or logical values."

the warnning sign was one the ux(i,1) = ux(i,1) + (x(i,j)- x(i,i)); line

   % FILL THIS PART
    % Compute consensus
    for i = 1:N
        n(N,i)= indegree(G,i)
        for j = n(N,i)
            ux(i,1) = ux(i,1) + (x(i,j)- x(i,i));
            uy(i,1) = uy(i,1)+ (y(i,i)-y(i,j));
        end
    end

[Matt J]

You have to handle the case where the indegree is 0.