release structure

Dear all:

I try to set a separate file for parameters in a model, and I want to retain their name so later on I can do sensitivity analysis using string comparison to identify the parameter name. So I define my parameters into structures, such as:

param.eps = 6;                         
param.beta = 0.99;                          
param.theta = 0.7532;                       
param.gamma = 0.5;

I want to release the structures into into variables as the following:

eps = 6;                         
beta = 0.99;                          
theta = 0.7532;                       
gamma = 0.5;

Is there an automatic way for doing this? I suspect I can setup the structure contains the name and value separately, and I probably can run a loop to equate the name with the value. But I think there must be a quicker and better way of doing this...

Any comments will be appreciated.

Cheers

Ben

Answer 1

[Jan]

Staying at the structs has some benefits if you use dynamic field names:

param.eps = 6;
param.beta = 0.99;
param.theta = 0.7532;
param.gamma = 0.5;

fields = fieldnames(param);
for i = 1:length(fields)
  aField = fields{i};
  fprintf('%s = %g\n', aField, param.(aField));
end

If you assign the variable "eps" dynamically, you will overwrite the built-in function with the same name. Such tricks will impede the debugging dramatically!

But if you really have a really good reason to need this really:

function FieldToVar(S)
F = fieldnames(S)
for i = 1:length(F)
  aF = F{i};
  assignin('caller', aF, S.(aF));
end

This is faster than an equivalent EVAL approach and less dangerous. Nevertheless, I think, this method is worse than using the dynamic field names directly.

Answer 2

[Oleg Komarov]

Why would you like to do such a thing?

% A method that avoids eval:

fnames = fieldnames(param);
save('param.mat','-struct','param')
load('param.mat')
delete('param.mat') % Or save it in the temp folder

[Ben Wang]

Hi Oleg:

I want the parameters to be identified by their names rather than matrix(or vector) index. This would help me alot later on when I do complex sensitivity analysis, so that I can change the value of the parameters by matching the names. (I guess the only benefit is a more intuitive code and less matching errors)

Thanks for replying

Ben

[Oleg Komarov]

Why can't you keep the structure. It's there for this reason and allows you to dynamically index the fields.