How to comparison decimal numbers

Hi all!

I have two matrices. They have one column. First matrix is:

7.551119
7.551154
7.551189
7.551224

Second matrix is:

7.551111
7.551146
7.551181
7.551215

I want to comparison two columns but only 5 decimal places. I don't like round my numbers like:

 7.55112
 7.55115

and so on, if I use the function round.

[Walter Roberson]

When you say that you want to compare to 5 decimal places, do you mean that when printed out rounded to 5 decimal places the numbers must match, or do you mean that the difference between the two numbers must be less than 10^(-5) ? Or at most 1/2 * 10^(-5) ?

[Thar]

I want to keep the 5 decimal points, but not rounded the numbers. for example for the number 7.551187 i want to keep only the 7.55118 and not round to 7.55119.

Answer 1

[arich82]

You can truncate (without rounding) using floor (or fix, if your numbers can be negative):

x = [ ...
      7.551119; ...
      7.551154; ...
      7.551189; ...
      7.551224; ...
    ];

y = fix(x*1e5)/1e5;

output:

y =

     7.551110000000000
     7.551150000000000
     7.551180000000000
     7.551220000000000

[Thar]

Thank you!!

Answer 2

[Image Analyst]

You need to use a tolerance. See the FAQ for a complete explanation: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

Answer 3

[Thorsten]

You can round to 5 decimal places using

xr = round(x*1e5)/1e5;

You may want to set

format long

such that the result is properly displayed.

[Image Analyst]

Or simply

xr = round(x, 5);

unless one is using an antique version of MATLAB.

[Walter Roberson]

1.234563 rounds to 1.23456

1.234565 rounds to 1.23457

but the numbers differ by only 0.000002

This is why it is necessary to know whether the question is about whether the values are equal when rounded or if the question is whether the values differ by less than a threshold.

[Thar]

The question is whether the values are equal, but i don't like to round the values. for example if i have the values 7.551119 and 7.551111 i want to keep for each value 5 decimal points, 7.55111 and 7.55111.These values are equal and this is i want. If i round the values the first value will be 7.55112 and the second is 7.55111.I don't like this.

[Image Analyst]

Then don't round (as I suspected you shouldn't). Use the tolerance like I told you in my answer where I referred you to the FAQ.

[Walter Roberson]

To check, Thodoris, you are okay with 7.551111 comparing equal to 7.551119, but 7.551119 should not compare equal to 7.551121 even though that is closer to it than 7.551111 is?