Variable not found in parfor loop

If I run the script:

z=1:1000;

parfor i=1:numel(z)
    zfun(z(i))
end

which calls the function:

function zfun(z)

for j=1:50
    for k=1:100
        myz=z*10+myz*k;
    end
end

save(fullfile('filepath', num2str(myz)), 'myz');

end

I get an error of Undefined function or variable 'myz' for the save command.

Any ideas how to fix this?

[Walter Roberson]

Which MATLAB version?

My spidy-senses are suggesting you might be using R2015b or R2016a but not R2016b ?

[JohnDylon]

R2016b trial for Linux. (No error for 2014a on PC though!)

Answer 1

[Walter Roberson]

You do not initialize the variable in the zfun loop.

[JohnDylon]

Initializating "myz=[]" outside of the zfun loop and passing it through the function as zfun(z(i), myz) done the job. Thanks again!

[Walter Roberson]

There should not be a need for that; you should be able to just initialize it to 1 inside zfun.

Initializing to [] is going to result in a lot of multiplying with the empty matrix, which will not be productive.

[JohnDylon]

Then you say

function zfun(z)
 myz=1;
 for j=1:50

      for k=1:100
          myz=z*10+myz*k;
      end
  end
  save(fullfile('filepath', num2str(myz)), 'myz');
  end

is better to do?

[Walter Roberson]

Yes, that would have less overhead. However, due to finite precision of floating point numbers, the result of the above is going to be -inf below about -1/17 and +inf above it. The zero is at about -0.058197670686932642438500200510901 . If you were trying to find the zero, it would be much more effective to use the symbolic toolbox.

[JohnDylon]

Thank you for all valuable guidance.