Check if element in array are square of each other

Hello,

I have a problem where I have to find possible squares in an array. For example [7 5 49] or [49 5 7] is true since 7 squared is 49, but [11 13 25] should return false.

Is there a way to do it better than a nested loop?

Thank you!

function y = isItSquared(x)
    y = false; 
    
    for i = 1:length(x)  
        for j = i+1:length(x)
            if x(i)^2 == x(j) || x(i) == x(j)^2
                y = true
                break
        end
        
    end
    
end

Answer 1

[Mark Sherstan]

You can get rid of one of the for loops:

function y = isItSquared(x)
    y = false;
    xSquare = x.^2;
    
    for ii = 1:length(x)
        if (sum(x(ii) == xSquare) ~= 0)
            y = true;
            return
        end
    end
        

[am]

I don't get how this checks every element in the array?

[Mark Sherstan]

It loops through the original x and sees if it is anywhere in the xSquare variable. So if we had:

x = [2 7 49]

xSquare = [4 49 2401]

The loops would look like:

sum([0 0 0]) --> 0

sum([0 0 0]) --> 0

sum([0 1 0]) --> 1

Since we are checking if the variable is not equal to zero (~=) then the last instance is the only one that would satisfy the if statment and return the function.

[am]

So if xSquare has no index, it means that the whole array is checked?

sum(x(ii) == xSquare) ~= 0

[Mark Sherstan]

Correct, it is a boolean check returning an array of 1's or 0's.

Answer 2

[madhan ravi]

nnz(V.^2==V.')>=1 % where V your vector, result 0 means false, 1 means true

[madhan ravi]

For versions prior to 2016b:

nnz(bsxfun(@eq,V.^2,V.'))>=1 

[madhan ravi]

So your function file would be:

function y = isItSquared(x)
    y = nnz(bsxfun(@eq,V.^2,V.'))>=1 ; 
end

And for calling the function:

V=[7 5 49];
y = isItSquared(V)

[am]

Thank you so much.

I am new to matlab. What are all the sub commands you are using?

nnz(bsxfun(@eq,V.^2,V.'))>=1 ;

what is nnz

what is bsxfun?

and @eq? why the arrowbase?

[madhan ravi]

@eq means equal ,see https://in.mathworks.com/help/matlab/ref/bsxfun.html for further explanation.

https://in.mathworks.com/help/matlab/ref/nnz.html - nnz() gives you the total number of non-zero elements.

>= means if you have one or more then set it to true.

So what happens is each element of the vector is compared with the square of each element , so if atleast a single match is found then the answer returned is 1 meaning true.

[am]

I think it was a fantastic answer as well, thank you!

Answer 3

[Steven Lord]

I would probably do this using some subset of the ismember, any, sum, all, and/or isequal functions. Read through the help text and see if you can think of a way to use some of those functions to accomplish that task.

Answer 4

[KSSV]

a = [7 5 49] ;
b = [49 5 7] ;

idx = a.^2==b

In idx if 1 , true, if zero false.

[am]

Hello,

There is only one array being fed to the function.

Answer 5

[Agam Sharma]

function b = isItSquared(a)  
b=false;
  c=a.^2;     %creating another array containing respective squares in 'a'
  for i=1:length(c)
      if(ismember(c(i),a))   %check if square is present in a itself
          b=true;
      end
  end
end