Store variables from a loop to use later

Hi, I have this simplified version of a script I am trying to run. I have a range of variables I want to run through an equation ('Answer' in this case). I have determined that I only want solutions that produce a value less than 10, I want to store these values in an array so that I can check they provide the correct solution, along with allowing me to do further calculations later on. Currently I have used display to print the i,j,k values and then copy and paste them into a vector. This is rather tedious and I am struggling to get the values to be stored in an array.

clear,clc
w = [9 8 7];
x = [1 2 3];
y = [3 2 1];
Answer = zeros(length(w),length(x),length(y));
for i = 1:length(w)
    for j = 1:length(x)
        for k = 1:length(y)
            Answer(i,j,k) = w(i)*x(j)*y(k);  
            if Answer(i,j,k) <= 10 
               disp([num2str(i),',',num2str(j),',',num2str(k)]) %displays the order of i,j,k that produces a desired solution
               
               Var = zeros(length(Answer),length(Answer));
               Var(i,:,:) = [i j k]; % Vector with variables in order than produces solution
            end
        end
    end 
end
for l = 1:length(Var)
    for m = l+3
        for n = m+6
            Values = w(Var(l))*x(Var(m))*y(Var(n)); %Verify that the variables produce correct solution
        end
    end
end

Currently the i,j,k values that give a solution less than 10 are 1,1,3 | 2,1,3 | 3,1,3

When I try to store this in Var the array is rewriten each time meaning that I can only confirm the last configuration in the next for loop, i.e. Var = [0 0 0;0 0 0;3 1 3]

If anyone can help with this, it would be gladly appreciated

Answer 1

[David Fletcher]

The line in the k loop:

Var = zeros(length(Answer),length(Answer));

This overwrites all values in Var with zeroes on every iteration of the k loop (except the last). The preallocation would need to be moved outside all loops (like your preallocation for the Answer var). Either that or just grow it dynamically - although it's not good programming practice as it has a lot of time and memory overhead, but as a quick hack to get things working it is an easy alternative, and unless the data set is large you probably won't notice much.

[Brandon Ratter]

Thanks, I have tried moving it outside the loop and it creates the array that I need. However if I increase the accepted value range to 20, the number of variuables obviously increases. When I run it with a reange of <= 20 the array does not store the other 6 variations, only the first 3. how could I change the set up of the array Var to log the additional values no matter what the range is?

[David Fletcher]

Looking at it, I am slightly confused as to why you need the third dimension on the Var matrix. Surely, it only needs to be two dimensions. Saying that, the reason you are only getting three entries in your Var matrix, is because the i indexer is based on the length of the w vector (3), so there is no way on earth you can ever have more than three entries. You will need to change the way you index the answers into this matrix (maybe base it on a count that starts at one and increments every time you add something into it)

Something like this:

clear

w = [9 8 7];
x = [1 2 3];
y = [3 2 1];
count=1;
Answer = zeros(length(w),length(x),length(y));
for i = 1:length(w)
    for j = 1:length(x)
        for k = 1:length(y)
            Answer(i,j,k) = w(i)*x(j)*y(k);  
            if Answer(i,j,k) <= 20 
               disp([num2str(i),',',num2str(j),',',num2str(k)]) %displays the order of i,j,k that produces a desired solution
               
               %Var = zeros(length(Answer),length(Answer));
               Var(count,:) = [i j k]; % Vector with variables in order than produces solution
               count=count+1;
            end
        end
    end 
end

This gives

Var =

1 1 2

1 1 3

1 2 3

2 1 2

2 1 3

2 2 3

3 1 2

3 1 3

3 2 3

[Brandon Ratter]

In the more complex script I am using 5 variables so I made an Array based on all 5 variables, but now that you mention it, you are correct its far easier to have it as 2 dimensions. I've made the changes to both this script and the more lengthy one for my project and they both work well. Thanks for your help.