Variable 'a' is undefined on some execution paths. Why?

I'm using the block named Embedded MATLAB (that link the simulink to matlab) and when I try to run the code above, return the message error: "Variable 'a' is undefined on some execution paths". Besides that, other message appears: "Parsing successful for machine: "teste1_05mar13"(#17)" What does it mean?

function y = fcn(ia,va,t)
%#eml
p = ia*va;
N=1000;
if t <= 1.0e-6
  a = 0;
  b = 0;  
end

b = a-0.01; %"b" is the value of the same "a", but is a value that precedes in 0.01 the value "a"
a = b + (p -b)/N;
y=a;

Thanks

[Caroline Rosa]

function y = fcn(ia,va,t)
p = ia*va;
N=1000;
if t <= 1.0e-6
  a = 0;
  b = 0;  
end
b = a-0.01; 
a = b + (p -b)/N;
y=a;

In order to understand better. thanks

Answer 1

[Azzi Abdelmalek]

when if t <= 1.0e-6 is false a and b are unknown

You should declare a and b persistent

[Azzi Abdelmalek]

function y = fcn(ia,va,t)
persistent a b;
if isempty(a)   % Initialization
  a=0;
  b=0;
end
p = ia*va;
N=1000;
if t <= 1.0e-6 a = 0; 
  b = 0; 
end
b = a-0.01;
a = b + (p -b)/N;
y=a;

[Caroline Rosa]

thanks for your help Azzi. now it works. Thanks so much

[Alejandro Zavala]

Hi I want to run this code about MPPT

    %%%%
function D=inc(V,I)
Dinit=.574;
deltaD=0.001;
persistent Va  Da Ia;
if isempty(Da)
    Va=42.64;
    Ia=2;
    Da=Dinit;
end
dV=V-Va;
dI=I-Ia;
if dV== 0
    if dI~=0 
    else
        if dI>0
            D=Da-deltaD;
        else
            D=Da+deltaD;
        end
    end
else
    if dI/dV==-I/V
    else
        if dI/dV>-I/V
        D=Da-deltaD;
        else
        D=Da+deltaD;
        end
    end
end
Da=D;
Va=V;
Ia=I;

but Matlab shows this error

Variable 'D' is not fully defined on some execution paths.

Answer 2

[Ryad BOUKHARI]

Hello,

I faced the same problem, and it works.

Thank you Abdelmalek.