is this a bug?

I try to write a very simple program like this

function [ey]=check()
  ex=2;
  F=[[0 0 0.26 1.3];[0.6 0 0.86 1.3];[1.2 0 1.46 2.6];...
      [1.8 0 2.06 2.6];[2.4 0 2.66 2.6]];    % [x1 y1 x2 y2 Mat q]
    fanzahl=length(F(:,1)); % 5
    X=abs(F(1:fanzahl,3)-F(1:fanzahl,1));% x-length of every F 
    Y=abs(F(1:fanzahl,2)-F(1:fanzahl,4));% y-length of every F
    ey=abs(ex*Y./X); 
    for i=1:fanzahl
  p(ey(i));
  end
  end
  function []=p(ny)
  ny
  0:ny
  end

and I want to output the ny and 0:ny in the subroutine. after calculation I get this.

ny =

    10

ans =

     0     1     2     3     4     5     6     7     8     9    10

ny =

    10

ans =

     0     1     2     3     4     5     6     7     8     9    10

ny =

    20

ans =

Columns 1 through 14

     0     1     2     3     4     5     6     7     8     9    10    11    12    13

Columns 15 through 21

    14    15    16    17    18    19    20

ny =

    20

ans =

Columns 1 through 14

     0     1     2     3     4     5     6     7     8     9    10    11    12    13

Columns 15 through 21

    14    15    16    17    18    19    20

ny =

   20.0000

ans =

Columns 1 through 14

     0     1     2     3     4     5     6     7     8     9    10    11    12    13

Columns 15 through 20

    14    15    16    17    18    19

can you see? the last ny change to 20.000, and 0:ny is only to 19 not 20. is this a bug? I make something wrong?

Answer 1

[C]

ex=2;
F=[[0 0 0.26 1.3];[0.6 0 0.86 1.3];[1.2 0 1.46 2.6];...
    [1.8 0 2.06 2.6];[2.4 0 2.66 2.6]];    % [x1 y1 x2 y2 Mat q]
fanzahl=length(F(:,1));
X=abs(F(1:fanzahl,3)-F(1:fanzahl,1));
Y=abs(F(1:fanzahl,2)-F(1:fanzahl,4));
ey=abs(ex*Y./X);
for i=1:fanzahl
ey(i)
0:ey(i)
end

when I write it more simple, the answer is the same.

Answer 2

[the cyclist]

If you type

 >> format long

before you run your function, you will see that in the last case, ny is slightly less than 20, which is why you get the output you see.

[C]

thanks.

but ey(5) should be 20.000000 not 19.99999982

[the cyclist]

This is not a bug, but it is an issue with exact representation of floating-point numbers in computers. Here is some detailed documentation from Mathworks:

http://www.mathworks.com/support/tech-notes/1100/1108.html.

You could round "ny" to the nearest integer to get what you want.

[the cyclist]

Here is another place to read more about this issue:

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

Answer 3

[C]

yes, I know, but ey(5) should be 20.000000 not 19.99999982

X =

   0.260000000000000
   0.260000000000000
   0.260000000000000
   0.260000000000000
   0.260000000000000

Y =

   1.300000000000000
   1.300000000000000
   2.600000000000000
   2.600000000000000
   2.600000000000000

ey =

10.000000000000000
10.000000000000000
20.000000000000000
20.000000000000000
19.999999999999982