How to reset variables before each iteration

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Mekala balaji 2016-5-25

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回答： Charles Robinson 2022-2-18

Hi,

I have many variables, and I want to reset all variables except two variables before each iteration. Can anyone kindly tell how to do this.

Many thanks in advance

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Stephen23 2016-5-25

clear-ing variables slows your code down. The best plan would be to simply reallocate to those variables in each loop, so clearing is no required.

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Answer 1

Charles Robinson 2022-2-18

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I assume it is inefficient to clear variables, so better to simply overwrite as noted above: e.g.

A = A0; or

A = zeros(sizeofA)

If you are "building" the data (i.e. changing the variable size with each iteration, not recommended), or if sparsely initializing a matrix, you need to remove any values that may be lingering, e.g.:

A = []; A(idx) = A0;

I don't know if "emptying" is better than clearing A. Try both and let us know!

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Answer 2

Jos (10584) 2016-5-25

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I think I miss the point, but this will do what you are asking for:

    A0 = 7 ;
    B  = 1 ;
    for k=1:10 % iteration
      A = A0  % reset one variable
      B = k*A + 2*B + k % calculations that change another variable
    end

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Answer 3

Are Mjaavatten 2016-5-25

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Here is an example that clears all variables except b and c:

 % Fist create some variables
a = 1; 
b = 2;
c = 3;
d = 4; 
e = 5;
%
% The cell array keepvars should contain the names of all variables 
% that you want to keep, plus the variables that you need in the process:
keepvars = {'b','c','keepvars','ix','varlist'};
varlist = whos;
for ix = 1:length(varlist)
    if ~strcmp(varlist(ix).name,keepvars)
        clear(varlist(ix).name);
    end
end
% Finally, clear the intermediate variables:
clear ix varlist keepvars

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Are Mjaavatten 2016-5-25

I should add that although this may (or may not?) answer your question, it is not an example of good programming practice. It would be better to write your iteration code in such a way that there is no need to clear or reset variables.

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