Why do i get "Array indices must be positive integers or logical values." error?

Question

Endrias 2018-6-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/403528-why-do-i-get-array-indices-must-be-positive-integers-or-logical-values-error

评论： Endrias 2018-6-1

采纳的回答： Walter Roberson

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I keep getting this error from this function. Does anyone have an idea what is really happening?

%% SIMULATION

function [sys,x0,str,ts] = ctrl_sliding_mode(t,x,u,flag)
switch flag
    case 0
        [sys,x0,str,ts]=mdlInitializeSizes;
    case 3
        sys = mdlOutputs(t,x,u);
    case {2,4,9}
        sys=[];
    otherwise
        error(['Unhandled flag = ',num2str(flag)]);
end
function [sys,x0,str,ts]= mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates = 0;
sizes.NumDiscStates = 0;
sizes.NumOutputs = 3;
sizes.NumInputs = 6;
sizes.DirFeedthrough = 1;
sizes.NumSampleTimes = 0;
sys = simsizes(sizes);
x0 = [];
str = [];
ts = [];
function sys = mdlOutputs(t,x,u)
lvp_ref   = u(1);  %REFERENCE SIGNAL 
dlvp_ref = u(2);
lvp = u(3);
beta = u(4);
zeta = u(5);
dlvp = u(6);
eta = 0.2;
c  = 10;
e  = lvp - lvp_ref;
de = dlvp - dlvp_ref;
s  = c*e;
M=2;
if M==1
     ut  = 1/(c*beta*lvp^zeta)*(-eta*sign(s) + c*dlvp_ref);
elseif M==2 %Saturated function
    delta=0.2;
    kk = 1/delta;
    if abs(s)>delta
        sats = sign(s);
    else
        sats=kk*s;
    end
    ut  = 1/(c*beta*lvp^zeta)*(-eta*sats(s) + c*dlvp_ref);
end
   sys(1) = ut;
   sys(2)= e;
   sys(3) = de;

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Endrias 2018-6-1

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@Sandro Sats(s) is a function like sign(x) i.e. peicewise. And when i choose e.g. M = 1, i get the next error eventhough i see that a vector of length 3 is passing put as an output...

An error occurred while running the simulation and the simulation was terminated Caused by: Output returned by S-function 'ctrl_sliding_mode' in 'sim_sliding_mode/S-Function' during flag=3 call must be a real vector of length 3;

Sandro Lecci 2018-6-1

What is supposed to do the function sats? According to your if loop when M==2, sats is a variable that stores either the sign of s or the multiplication between s and kk (variables as well).

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Answer 1

Walter Roberson 2018-6-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/403528-why-do-i-get-array-indices-must-be-positive-integers-or-logical-values-error#answer_322780

s = c*e but c=10 and e = lvp - lvp_ref but lvp_ref is scalar and lvp = u(3) . So lvp is scalar and so e is scalar and so s is scalar. That would make sign(s) a scalar, and with kk being scalar, kk*s would be a scalar. So sats is a scalar. But you have sats(s) in the ut calculation, which is an indexing request.