embedded matlab function error message

i have this error message

"Output argument 'dvref' is not assigned on some execution paths."

when executing this code

function dvref =IC(V,I)
persistent Vref Vold Iold c;
if isempty(Vold)
  Vold=0; %initialized only once in the beginning
end
if isempty(Iold)
  Iold=0; %initialized only once in the beginning
end
if isempty(c)
  c = .1; %initialized only once in the beginning
end
if isempty(Vref)
  Vref=.5; %initialized only once in the beginning
end
dI=I-Iold;
dV=V-Vold;
if V==Vold
  if I~=Iold
  elseif I>Iold
      dvref=Vref-c
  else dvref=Vref+c
  end
elseif dI/dV~=-I/V
  if dI/dV > -I/V
      dvref=Vref-c
  else
      dvref=Vref+c
  end
end
Iold=I
Vold=V

Answer 1

[Walter Roberson]

In your "if I~=Iold" case you do not assign anything to dvref .

[mado]

actually this is not the problem i tried it but in a vain , error is still there.

Answer 2

[mado]

the answer is that dvref should be outside the if condition but in my flowchart it'snot outside the if condition ,so i don't know how to implement it any one help

Answer 3

[Azzi Abdelmalek]

Are you sur one of these two expression

• if V==Vold
• elseif dI/dV~=-I/V

is true for each step?

[mado]

yes, its true here is a link for the flowchart http://www.mediafire.com/view/?2tkvty7sq9d419o

[Azzi Abdelmalek]

Your code don't correspond to your chart

[mado]

why ?? what is the problem could you explain or modify this code?

[Azzi Abdelmalek]

From your chart, you should do

if V-Vold>0
   %your code1
else
   %your code2
end

[mado]

that's what i exactly did , but cause i don't know how to write if I- Iold==0 return i wrote if I ~=Iold and so on the other branch

[mado]

do you have any suggestions ?

[Azzi Abdelmalek]

Explain, clearly what you don't know to write?

[Azzi Abdelmalek]

From your chart :

 if V>Vold
    if I-Iold==0
        %do
    else
        if I>Iold
            dvref=Vref+c
        else
            dvref=Vref-c
        end
    end
    %-------------------------------
else
    if dI/dV==-I/V
        %do
    else
        if dI/dV > -I/V
            dvref=Vref+c
        else
            dvref=Vref-c
        end
    end
end

[mado]

 if I-Iold==0
      %do
do what ??i won't do any thing just i will return to measure i and v and this is not the problem we went far away from the original problem that dvref should be assigned outside if condition , since you saw the flowchart there is no place for dvref outside if condition

[Azzi Abdelmalek]

just let it as a comment, to make your code readable. The problem is that your code don't correspond to your chart. I've tried to fix it, try it and tell me about it

[mado]

what about the error message "Output argument 'dvref' is not assigned on some execution paths."

[Azzi Abdelmalek]

Well, you said if I-Iold==0, I won't do any thing which means, when the previous expression is true, there is no assignation to your variable dvref. Maybe you should assign to it the previous value or declare it as persistent.

[mado]

dvref can't be declared on persistent as it is the output of the embedded function.

[Azzi Abdelmalek]

You can use a unit delay block to get the previous value of dvref. Name it dvref_old, then in your code instead of "Doing nothing" you will do:

dvref=dvref_old

Answer 4

[mado]

if I-Iold=0 if yes return if no check the next step i don't know "return" here is right or not, so i reversed it i checked the inequality and so on

[Walter Roberson]

You cannot just return without having assigned something to dvref .

[mado]

ok , how to do this using simulink i think it will be easier