How can i create an array whose length indirectly depends on parfor loop's index?

As the title says, i want to ask if there is an elegant way to create an array whose length is indirectly related to the index of a parfor loop in a certain way.

The following code lines give me the error "size input must be integers". I'm sure the error is due to me trying to create the zero array K whose length is N (which, unfortunately, indirectly depends on the corresponding index of the parfor loop).

lambda = [10, 70, 20, 15];
parfor i = 1:length(lambda)
   N = lambda(i);
   K = zeros([1,N]);
end

Answer 1

[Edric Ellis]

Strange, that code works as written for me, so I'm not sure what's going wrong for you. But even so, I don't think it would do what you wanted - the variable K is a parfor temporary variable. A temporary variable is one which is fully assigned to on each iteration of the loop, and its value is not available after the loop completes.

I suspect that what you wanted was a parfor reduction variable, like so:

output = [];
parfor idx = 1:3
  newValues = (1:idx) .* (10 .^ (idx-1));
  output = [output, newValues];
end
disp(output)

which results in

     1    10    20   100   200   300

Reduction variables like output above allow you to accumulate values - often through concatenation (as shown above), or addition.

[Bui Tuan]

Hi Edric, thank you for your answer. I put the wrong code lines to the question actually. The original ones are something like this:

lambda = 0.1:0.1:1.2;
T = 1000;   M = 24;
parfor i = 1:length(lambda)
   N = M*T*lambda(i);
   K = zeros([1,N]);
end

Also, i have found that the error is NOT caused by parfor, but for some reason the calculated N was NOT an integer. For example, using that code, i get N = 7.2000e+03 (which is not an integer) when lambda(i) = 0.3, instead of 7200 and as a result, the error shows up when i try to create K.

Still, I don't know what is causing N to not be an integer sometime.

[Steven Lord]

You're encountering round-off error.