Parfor problems about loopVar = initVal:endVal

Greetings,

I got an error in my codes with line "parfor m=1:s", which is very weird. I don't know what happens. Can anyone give me some suggestions? Thank you!

Error using DynSys (line 11)
Unable to perform assignment because the indices on the left side are not compatible with the size of
the right side.
Error in eGram (line 37)
    parfor m=1:s
Error in testEGram (line 188)
EmGramian = eGram(@DynSys,[50; numel(index)],X0,0) ; 

My function is :

function xhat = eGram(Func,ParaVector,X0,flag) 
% xhat = obsv_gram_cov_unscaled(OdeFcn,Tspan,ParaVector,OuptputIndex,uss,xss) 
% Func: the ode function of the system
% Tspan: [start time, ending time, sampleLength]
% ParaVector: StateNumber n, OutputNumber k, 
% Cm: CmValue, and s = size(Cm,1) 
% OutputIndex: the indices of outputs corresponding to states
% uss: the value of input at steady state
% xss: steady state
% Orientation Number r 
% flag == 0, use initial state as bench (static); ~=0, use Y0 as bench (dynamically)

Tol			=	1E-9;

% gramian parameters
n = ParaVector(1);
k = ParaVector(2);

% initialization for T for observability
T(:,:,1) = eye(n,n);
Cm = logspace(log10(0.01),log10(1),5) .';

e = eye(n,n);
xhat = zeros(n,n);
s = length(Cm);
r = size(T,3);

Ts = 0.1;
nu = 600;
[~,~,Y0] = Func(X0);

for l=1:r
    parfor m=1:s    % ERROR THROWS HERE!!!!!
        chsi = zeros(n,n); 
        z = zeros(n,nu*k);   
        for i=1:n
        
            % apply perturbed initial condition
            initvalue = X0 + Cm(m)*T(:,:,l)*e(:,i);
   
            [t,X,Y] = Func(initvalue);
            
            if flag==0
                for iii = 1:k
                    z(i,nu*(iii-1)+1:nu*iii) = (Y(:,iii) - Y(1,iii))';
                end
            else
                 for iii = 1:k
                    z(i,nu*(iii-1)+1:nu*iii) = (Y(:,iii) - Y0(:,iii))';
                end
            end
                
        end                
                
        chsi = z*z';
        xhat = xhat + 1/(r*s*Cm(m)^2)*Ts*T(:,:,l)*chsi*T(:,:,l)';
    end
end

[Dinesh Yadav]

Is it throwing error if you are not using parfor?

[Matt J]

Do you get any errors if you replace your parfor loop with a regular for loop?

[Xin Shen]

I don't get any error if I use regular for loop

Answer 1

[Xin Shen]

I found that "Error using DynSys (line 11)" is caused by global variables. For parallel computation, I cannot use global variables.

Answer 2

[meghannmarie]

You are setting the variable xhat in the parfor and using the prevous itereation of xhat. You need to just access and set a slice of xhat, you cannot access and change xhat as a whole while other workers in parfor are accessing it. For example:

xhat(m,:) = xhat(m,:) + ...

[Xin Shen]

Thank you, I will try your suggestions and give you feedback!

[Xin Shen]

It does not work.

I got Error: The variable xhat in a parfor cannot be classified.

[meghannmarie]

Can you give some example inputs for Func, ParaVector, X0? Also what did you set xhat to in last line?

[Xin Shen]

I solved the problem of the Func because I use some global variables in Func.

Currently, the error is what you said about xhat. It seems that I cannot slice output xhat.