Arrays of unknown size as input

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Destro Katramis 2020-6-1

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编辑： Destro Katramis 2020-6-1

Hello everyone,

I want to have an input of 2 arrays which will either be inputed number by number from the user or as a desired range and step. That means that the array sizes won't be known a priori. Thanks a lot in advance!

For clarification:

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Mohammad Sami 2020-6-1

You have to consider what kind of calculations are you doing on your inputs.

As long as your calculations accept variable length inputs, the dimensions would not matter.

Example if you are doing element wise calculation, the dimensions would not matter.

Destro Katramis 2020-6-1

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Thanks a lot for your answer Mohammad!

The code is looking like this:

x=1:100;
y=1:200;
n=length(x);
k=length(y);
count=0;
for i=1:n
    for j=1:k
        c=sqrt(x(i)^2+y(j)^2);
        if c==fix(c)
            count=count+1;
            pyth(1,count)=x(i);
            pyth(2,count)=y(j);
        end
    end
end

And I would like to remove the first two lines and replace them with the inputs of the user (following the procedure as stated above).

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Answer 1

KSSV 2020-6-1

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You need not to worry about the dimensions of input. You can do what you wanted without loop. Check the below code.

[X,Y] = meshgrid(x,y) ; 
C = sqrt(X.^2+Y.^2) ; 
idx = C == fix(C) ; 
pyth = [X(idx) Y(idx)] ; 

So if your question is to ask, how to initialize an unknown array. You can do the following.

x=1:100;
y=1:200;
n=length(x);
k=length(y);
count=0;
pyth = NaN([],2) ; % as you know there are two columns
for i=1:n
    for j=1:k
        c=sqrt(x(i)^2+y(j)^2);
        if c==fix(c)
            count=count+1;
            pyth(count,1)=x(i);
            pyth(count,2)=y(j);
        end
    end
end

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Destro Katramis 2020-6-1

Thanks a lot for your answer KSSV and cudos for the first part, it reduced the number of lines by a significant amount!

If I understand your suggestion correctly, my question is not about the initialization of the array "pyth" before the loop, but as to how to ask the user for input concerning the arrays "x" and "y" (which can be of any size or entered number by number).

KSSV 2020-6-1

Ohh....that is pretty simple. Read about the function input.

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Arrays of unknown size as input

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