Undefined function or variable?

I have this code any problema than you can find?: I'm using MatlabFcn in simulink

 function out = fcn(qp, tao)
 fc=8.955;

 fv=5.234;

 fs=18.617;

 vs=0.145;

 delv=1.032;

 delt=0.172;

 ts=0.888;

 fk=(fc*sign(qp))+(fv*qp);

 if qp == 0 && abs(tao)< fs

 fq= tao

 end

 if qp == 0 && abs(tao)>= fs

 fq=fs*sign(tao)

 end 

 if qp ~= 0

 fq=fk

 end

 out = fq;

But even when "fq" has a value always. I can't play the program.

Undefined function or variable 'out'. The first assignment to a local variable determines its class.

Function 'ImpovedStaticCoulombViscous' (#133.132.135), line 10, column 4: "out" Launch diagnostic report.

Answer 1

[Walter Roberson]

Your code does not define fq in the case that qp is nan.

When you are constructing MATLAB Function blocks, it is safest to start by assigning the output zeros() of the appropriate size and data type.

I also recommend that you code as

if qp == 0
  if abs(tao)< fs
    fq = fs;
  else
    fq = fs * sign(tao);
  end
else
  fq = fk;
end

this makes it obvious to the compiler that fq is assigned in every possible branch. (But give some thought to handling nan anyhow.)