Question

I would like to load variables from a text file.

For example, my text file, varA, varB, and varC.

In MATLAB, I would like to give these variables values so that every variable is a 2×2 matrix.

So from the text file containing the above information I would get a matrix that looks like this:

[ 1 2 3 4 5 6;   1 2 3 4 5 6] 

Is this possible?

I added a second example to try to make things a little clearer.

My text file, text.txt, looks like this

x1 x2 x3 

In MATLAB my .m file gives the values to these variables like

x1 = [1 1; 1 1] x2 = [2 2; 2 2] x3 = [3 3; 3 3] 

So, when I import my textfile I would get

a = (textfile) a = [1 1 2 2 3 3 ; 1 1 2 2 3 3] 

I basically try to adapt a genetic algorithm (GA) on a very huge problem (of travelling salesman problem (TSP) type). The problem is that every variable I have is a matrix and the crossover, fitness and mutation codes get pretty complicated. And I am having problems of making a random start population as well.

I would like to randomly select, let’s say 30 variables, from a list with 256 so that the variable can only be picked once. Each variable however have their own specific values in a 2*2 matrix that cannot be changed.

I would like to use randperm and then put an x before every value making them variables instead of values…

Answer 1

If the data in the text file looks like this (strings separated by spaces):

x1 x2 x3 ... 

You can read the strings into a cell array using TEXTSCAN like so:

fid = fopen('file.txt','r'); A = textscan(fid,'%s'); fclose(fid); A = A{:}; 

A now stores the strings in a cell array: {‘x1’; ‘x2’; ‘x3’; …}. Now, to make a variable out of one of these strings and assign it a value, I would use ASSIGNIN:

assignin('base',A{1},[1 2; 1 2]); 

This will create a variable x1 in the base workspace and assign it the value [1 2; 1 2]. The first argument can be either ‘base’ or ‘caller’ to create a variable in either the MATLAB base workspace or the workspace of the caller function. You would repeat this for each string name in A, giving it whatever value you want.

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ALTERNATE OPTION:

This is an alternate answer to the one I gave you above. The above answer addresses the specific problem you raised in your question. This answer gives you a whole other option to potentially avoid doing things the way you were describing them in your question, and it will hopefully make things easier for you…

If I understand your problem, you basically have 256 2-by-2 matrices, and you want to randomly pick 30 of them. Each of these 2-by-2 matrices sounds like it is stored in its own variable (x1 to x256). Instead, I would suggest storing all 256 matrices in just one variable as either a 3-D array:

xArray = zeros(2,2,256);     % Initialize all matrices as [0 0; 0 0] xArray(:,:,1) = [1 1; 2 2];  % This enters a value for the first matrix 

or a cell array:

xArray = cell(1,256);    % Initializes an empty array of cells xArray{1} = [1 1; 2 2];  % Enters a value for the first matrix 

You would have to initialize all the values first. Then if you want to randomly pick 30 values, you can next randomize the order of either the third dimension of the 3-D array or the order of the cell array by using RANDPERM:

startOrder = 1:256;              % The default order of the matrices index = randperm(256);           % Randomly order the numbers 1 to 256 xArray = xArray(:,:,index);      % For a 3-d array xArray = xArray(index);          % For a cell array 

Then just use the first 30 entries in xArray for your calculations (instead of the individual variables like you were before):

x = xArray(:,:,1);  % Puts the first matrix from the 3-D array in x x = xArray{1};      % Puts the first matrix from the cell array in x 

You can keep repeating the use of RANDPERM to keep generating new randomized arrays of matrices. If you have to keep track of which original matrices you are using, you have to add this line after you randomize xArray:

startOrder = startOrder(index); 

Now the entries of startOrder will tell you the original position a matrix was in. For example, if the first array entry in startOrder is 40, then the matrix in the first position of xArray was originally the 40th matrix you entered when you initialized xArray.

Hope this helps!