How to round the decimals to required digits.

If the values of a in double is

a=55.619999999999999;

I want to use "round" function i.e result = round(a,4); now my expected result should be result = 55.6199.

But round function is not working in MATLAB Got the below error

>> a=55.619999999999999

a =

55.619999999999997

>> round(a,4) Error using round Too many input arguments.

Any talented guys please help out.

Thank you in advance.

[KSSV]

round doesn't accept, any input other then single number. I think you should look into format.

By the way, you want to display that in file or command window?

[Thouheed Shaik]

Hi KSVV,

I want limit it to 4 decimals and use it for setting flags exactly at 55.6199

There is a command shown in matlab as below please go through the link provided

Link : https://in.mathworks.com/help/matlab/ref/round.html#buftps_-1

Try this Example

Round the elements of a vector to retain 2 significant digits.

format shortg
x = [1253 1.345 120.44]
x = 
         1253        1.345       120.44

y = round(x,2,'significant')
y = 
         1300          1.3          120

[Walter Roberson]

You are looking at the documentation for a release newer than what you have.

"and use it for setting flags exactly at 55.6199"

You will need to switch to the symbolic toolbox for that. MATLAB does not represent numbers in decimal. 55.6199 does not exist exactly in IEEE 754 binary double precision numbers.

Answer 1

[Walter Roberson]

The ability to supply a number of decimal places for round() was introduced in R2014b.

"now my expected result should be result = 55.6199"

You cannot get that except for presentation purposes. The internal representation of 55.619999999999999 is not 55 + 619999999999999 / 10^15 : the internal representation is equivalent to 55.61999999999999744204615126363933086395263671875 . The internal representation of 55.6199 is equivalent to 55.619900000000001227817847393453121185302734375

If you need 55.6199 exactly to be stored, you will need to switch to the symbolic toolbox.

[Thouheed Shaik]

Thank you for the information.

May be you are right, I was using R2013b, i will check in R2014b if round(x,n) is working or not.

Answer 2

[John]

Hi,

I think the rounded value (4 digits) for a would be a = 55.6200 (due to the trailing nines. If you want to dump the rest of the nines (truncate) to get a = 55.6299 you could use:

fix(a*1000)/1000

where a number of zeroes are the decimal points you want. Taken from https://se.mathworks.com/matlabcentral/answers/234470-truncating-a-number-without-rounding

Check this old post: https://se.mathworks.com/matlabcentral/answers/24638-round-towards-even-in-sprintf

I hope it helps...

[Thouheed Shaik]

Thank you so much john,

It was really helpful.