MATLAB: Best practice to pass large number of parameters to many functions

functionsparametersstyle

This a programming style question. I have to solve a model for given parameters. The parameters are fixed in the beginning and they do not change during execution. These parameters need to be available to all the functions and subfunctions of the code. So far I used global variables. This is not very elegant, but it worked. But when I tried to speed up my code with using "parfor" instead of "for", then I learned that globals and parfor don't play well together.

So now I am planning to pass all the parameters to all functions as input arguments. Obviously, I don't want to write out each of them and create functions with 20-30 inputs. What is the best practice to do this? Should I use a structure?

Thanks, Andras

Best Answer

Yes. Simplest and fastest would be to use a struct as a container. That way you pass around only one argument to each function where any parameter is needed. This is not costly in terms of space or time, since MATLAB does not copy the struct into each workspace unless it is modified there.

Another option which will surely be slower but does not need you to pass in anything, is to use a function. Have the parameters defined in there as persistent variables, which you could easily set up so they are passed in initially.

Then when you want to know the value of a given parameter, query the value using the name of that parameter. Let the function do the work here. It would be slower, but requires no passed arguments at all.

You could even set up a list of prefs with setpref, which you could then query the values using getpref. Of course, this would be even slower, since I think prefs are stored on disk.

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MATLAB: Scalar assignment and nargout bump

To me, a better justification (if there is one) for the nargout bump is to make it easier to write wrappers for the many builtin functions tht always return at least 1 argument, even when called with nargout=0. For example, at the command line, SORT always returns at least one output arg, even when one is not explicitly requested,

>> sort([5 1 3]) % call with no arguments
ans =
       1     3     5

Suppose I now want to write a wrapper for sort() such that its 2nd argument returns 0-based indices instead of 1-based indices. Then I can do so, while preserving the above behavior, as easily as

   function varargout=mysort(varargin)
    [varargout{1:nargout}]=sort(varargin{:});
    if nargout>1, varargout{2}=varargout{2}-1;
   end

whereas without the bump, I would have to do something more complicated,

   function varargout=mysort(varargin)
    [varargout{1:max(1,nargout)}]=sort(varargin{:});
    if nargout>1, varargout{2}=varargout{2}-1;
   end

to ensure that at least one output arg was always returned. To my tastes, I would rather endure the second syntax for consistency's sake, but maybe that's just me...

MATLAB: Interpreting varargin name-value pairs.

Yes... Use inputParser

Best Answer

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MATLAB: Scalar assignment and nargout bump

MATLAB: Interpreting varargin name-value pairs.

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