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I have calculated two one diensonal matrices (i.e. two arrays) using two different equations. I am trying to check if corresponding values of both the arrays are equal or not. Following are the two methods that I followed to generate two arrays, namely y1 and y2,

Method: 1

R = 2.5;

x = (0:0.005:1);

y1 = R*x.*(1-x);

Method: 2

x = (0:0.005:1);

y2 = (-1*((x-0.5).^2) + 0.25)/0.4;

I am using following command to check equality between the values of two arrays,

y1 == y2

It is expected that both the arrays should be equal but, the output of above command is a logical array consisting of both zero's and one's. I tried manually cheking the values and they were equal. For example, (I have kept format of command window as long)

>> format long

>> y1(3)

ans =

0.024750000000000

>> y(3)

ans =

0.024750000000000

Later on, I tried this,

>> y1(3)==y(3)

ans =

logical

0

If I explicitely set these values to other variables,

>> format long

>> a=0.024750000000000;

>> b=0.024750000000000;

>> a==b

ans =

logical

1

In the question I am talking about number of extra zeros after decimal point because, if I explicitely remove those zeros from the values of both the arrays (by opening the arryas in variables window), I get,

>> format long

>> y1(3)

ans =

0.024750000000000

>> y(3)

ans =

0.024750000000000

>> y1(3)==y(3)

ans =

logical

1

What is happening here? What am I missing?

How do I check the equality between the two arrays generated in such a manner?

Bruno Luong
on 15 Aug 2020

"How do I check the equality between the two arrays generated in such a manner? "

tol = 2*eps(norm(y1,Inf));

norm(y1-y2,Inf)<=tol

Sara Boznik
on 15 Aug 2020

Hi,

I also tried like you and also got wrong result. Later I checked for y1(201) where the ans=0 and I got correct result.

It is possible that is Matlab's bug.

Than I try also:

tf = isequal(y1,y2)

And also get logical 0.

But then I tried that:

y1 = struct('field1',0.005,'field2',2500);

y2 = struct('field2',2500,'field1',0.005);

tf = isequal(y1,y2)

And works, I got logical 1.

Best of luck.

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