Parfor problems about loopVar = initVal:endVal

Question

Xin Shen 2019-9-24

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/481918-parfor-problems-about-loopvar-initval-endval

回答： Xin Shen 2019-10-4

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

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Matt J 2019-10-3

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

Xin Shen 2019-10-3

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

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Answer 1

Xin Shen 2019-10-4

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https://ww2.mathworks.cn/matlabcentral/answers/481918-parfor-problems-about-loopvar-initval-endval#answer_394738

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

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Answer 2

meghannmarie 2019-10-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/481918-parfor-problems-about-loopvar-initval-endval#answer_394651

编辑：meghannmarie 2019-10-3

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,:) + ...