I have a series of variables form a1 to a100 and each one has a single numeric value. I want to repeat copies of that value to 1-by-4 matrix for all of them.

For e.g. a1 = 5; a2 = 6; ......a100 = 43; I want it to be like:- a1 = [5 5 5 5]; a2 = [6 6 6 6]; ... a100 = [43 43 43 43]; I know that, if the variables are too few then it is easily possible by individually using 'repmat'. But how to do it for these many variables?

[Bob Thompson]

Why do you need individual variables? I know that others will give you a comment about how having a variable name changing like you do (a1 a2 a3..) is considered a bad code practice, and it is better to just use a matrix. In your case you could make a 100x4 matrix where the four columns are repeats of each other, so instead of calling a1 you call the first row of a and get the same thing.

a = zeros(100,4);
a(:,1) = data;
a(:,2) = data;
a(:,3) = data;
a(:,4) = data;

>> a(1,:)
 ans  = 
      5 5 5 5

[Stephen23]

This would be trivial if you had sensibly put your data into one vector:

V = [5;6;...;43];
repmat(V,1,4)

Did you see what I did there? I wrote one simple line of code that does what you need, simply by designing the data better. Simpler, more efficient code through better data design! The best solution to your problem is to NOT have one hundred numbered variables in your workspace, but to design your data better.

You should fix however those hundred variables got into the workspace: possibly you just need to use indexing. Indexing is simple, neat, and very efficient, unlike what you are trying to do. Read this to know more:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[Ankit Singh]

Thanks for your replies, but I am doing mixed-integer linear programming, where I need the data in this way to be usable in the optimization function. If you have any way for this, then pls reply

[Stephen23]

"... but I am doing mixed-integer linear programming, where I need the data in this way to be usable in the optimization function."

You can probably use indexing. Please upload your code by clicking the paperclip button.

[Stephen23]

I don't see any reason why mixed-integer linear programming requires lots of separate variables: what optimization function are you using?

[Ankit Singh]

Guys thanks for your timely replies...but I found out that the approach I was using was not a viable option, but my objective is now fulfilled as I have changed my approach.

Answer 1

[Stephen23]

Your script Trial1.m (attached) is pointlessly complex, and using eval to access variables names just complicates things even more for no benefit. I doubt that this approach is worthwhile. Most of the first half can be replaced with just one line of code, and the second half is an inefficient use of eval to create lots of variables: keep your data in arrays and just use indexing!

Replace all of this:

load('unitCommData.mat','T','loadProfile');
load('DA_price.mat');
nHours = 24;
nIntervals = nHours*4;
DAPrice = zeros(nIntervals,1);
cnt = 1;
for i = 1:nIntervals
    DAPrice(i,1) = e_Auktion24Energie(cnt,1);
    if mod(i,4) == 0
        cnt = cnt + 1;
    end
end
DA_Price = repmat(DAPrice,1,4);

with the much simpler and more robust:

>> ucd = load('unitCommData.mat','T','loadProfile');
>> dap = load('DA_price.mat');
>> P = kron(dap.e_Auktion24Energie,ones(4))
P =
      31.72        31.72        31.72        31.72
      31.72        31.72        31.72        31.72
      31.72        31.72        31.72        31.72
      31.72        31.72        31.72        31.72
      28.63        28.63        28.63        28.63
      28.63        28.63        28.63        28.63
      28.63        28.63        28.63        28.63
      28.63        28.63        28.63        28.63
      27.86        27.86        27.86        27.86
      27.86        27.86        27.86        27.86
... more rows here
      35.44        35.44        35.44        35.44
      35.44        35.44        35.44        35.44
      35.44        35.44        35.44        35.44
      31.07        31.07        31.07        31.07
      31.07        31.07        31.07        31.07
      31.07        31.07        31.07        31.07
      31.07        31.07        31.07        31.07
      28.31        28.31        28.31        28.31
      28.31        28.31        28.31        28.31
      28.31        28.31        28.31        28.31
      28.31        28.31        28.31        28.31

The second half of your code can be simply replaced with this line:

>> X = repmat((1:size(P,1)).',1,4)
X =
     1     1     1     1
     2     2     2     2
     3     3     3     3
     4     4     4     4
     5     5     5     5
     6     6     6     6
... more rows here
    91    91    91    91
    92    92    92    92
    93    93    93    93
    94    94    94    94
    95    95    95    95
    96    96    96    96

Which you can trivially access using indexing. So far there is no reason why you require lots of magically named variables.

[Ankit Singh]

Thanks!! Great!!