Undefined variable error in nested function

I keep getting the error message "Undefined function or variable 'z'." when I run:

z = [0.388039 0.264102 0.185497 4.66E-02 2.58E-02 7.68E-03]; %Smoke 1
D = 10; %mg
V = 25;
t = [1.0 3.0 5.0 14.0 18.0 24.0];
k1 = [0 1];
[kv,kval]=fmin(k1,D,t,z);

which calls the function below:

function [kv,kval]=fmin(k1,D,t,z)
[kv,kval]=fminsearch(@fminfunc,k1);
  function f = fminfunc(kv)
  sum=0;
  for j=1:6
      sum = sum + z(j) - (D/kv(2))*exp(-kv(1)*t(j));
  end
  f = sum^2;
  return   
return

and I get this output:

Undefined function or variable 'z'.
Error in hw4c_1>fminfunc (line 22)
      sum = sum + z(j) - (D/kv(2))*exp(-kv(1)*t(j));

I'm not sure why the variable is undefined when I've already passed in the variables to the function. Please help

Answer 1

[Jan]

Did you see that MLint shows a warning for the 2nd return command? This should catch your attraction in case of problems.

The solution is easy: Close the functions with an end, not with return:

function [kv,kval]=fmin(k1,D,t,z)
[kv,kval]=fminsearch(@fminfunc,k1);
  function f = fminfunc(kv)
  S = 0;
  for j=1:6
      S = S + z(j) - (D/kv(2))*exp(-kv(1)*t(j));
  end
  f = S ^ 2;
  end
end

I've replaced "sum" by "S", because shadowing builtin function causes troubles frequently.

A simplification:

function f = fminfunc(kv)
f = sum(z - (D/kv(2)) * exp(-kv(1)*t)) ^ 2;
return

[Sabrina]

Awesome, thanks! I'm obviously a bit new to Matlab so simple problems like this always mess me up.

[Jan]

You are welcome. :-)