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round

Round to nearest decimal or integer

Description

example

Y = round(X) rounds each element of X to the nearest integer. In the case of a tie, where an element has a fractional part of 0.5 (within roundoff error) in decimal, the round function rounds away from zero to the nearest integer with larger magnitude.

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Y = round(X,N) rounds to N digits:

  • N > 0: round to N digits to the right of the decimal point.

  • N = 0: round to the nearest integer.

  • N < 0: round to N digits to the left of the decimal point.

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Y = round(X,N,type) specifies the type of rounding. Specify "significant" to round to N significant digits (counted from the leftmost digit). In this case, N must be a positive integer.

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Y = round(___,TieBreaker=direction) rounds ties as specified by direction. Use this argument after any of the input argument combinations in the previous syntaxes.

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Y = round(t) rounds each element of the duration array t to the nearest number of seconds.

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Y = round(t,unit) rounds each element of t to the nearest number of the specified unit of time.

Examples

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Round the elements of a 2-by-2 matrix to the nearest integer.

X = [2.11 3.5; -3.5 0.78];
Y = round(X)
Y = 2×2

     2     4
    -4     1

Round pi to the nearest 3 decimal digits.

Y = round(pi,3)
Y = 3.1420

Round the number 863178137 to the nearest multiple of 100.

round(863178137,-2)
ans = 863178100

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

X = [1253 1.345 120.44]
X = 1×3
103 ×

    1.2530    0.0013    0.1204

Y = round(X,2,"significant")
Y = 1×3
103 ×

    1.3000    0.0013    0.1200

The format command controls how MATLAB® displays numbers at the command line. If a number has extra digits that cannot be displayed in the current format, then MATLAB automatically rounds the number for display purposes. This display can lead to unexpected results when combined with the round function.

Consider the result of this subtraction operation, which displays 5 digits.

format short
x = 112.05 - 110
x = 2.0500

The displayed result is 2.0500, which looks like a tie. However, due to the floating-point arithmetic error, the tie at a fractional part of 0.5 is not within roundoff error.

Based on the displayed value of x, rounding x to 1 decimal should return 2.1.

y = round(x,1)
y = 2

In fact, the problem here is that MATLAB is rounding x to 5 digits for display purposes. The round function returns the correct answer. Confirm the answer by viewing x with format long, which displays x rounded to 15 digits.

format long
x
x = 
   2.049999999999997

For comparison, show the rounding results for a tie that is within roundoff error and for a tie that is not within roundoff error.

x1 = 2.05
x1 = 
   2.050000000000000

y1 = round(x1,1)
y1 = 
   2.100000000000000

x2 = 2.05 - eps(2.05)
x2 = 
   2.049999999999999

y2 = round(x2,1)
y2 = 
     2

Create a vector of decimals that have ties, that is, decimals with a fractional part of 0.5 (within roundoff error).

X = -2.5:1:2.5
X = 1×6

   -2.5000   -1.5000   -0.5000    0.5000    1.5000    2.5000

Round the ties to the nearest even and odd integers.

Yeven = round(X,TieBreaker="even")
Yeven = 1×6

    -2    -2     0     0     2     2

Yodd = round(X,TieBreaker="odd")
Yodd = 1×6

    -3    -1    -1     1     1     3

Round the ties towards positive and negative infinity.

Yplusinf = round(X,TieBreaker="plusinf")
Yplusinf = 1×6

    -2    -1     0     1     2     3

Yminusinf = round(X,TieBreaker="minusinf")
Yminusinf = 1×6

    -3    -2    -1     0     1     2

Round the ties away from zero and towards zero.

Yfromzero = round(X,TieBreaker="fromzero")
Yfromzero = 1×6

    -3    -2    -1     1     2     3

Ytozero = round(X,TieBreaker="tozero")
Ytozero = 1×6

    -2    -1     0     0     1     2

Round each value in a duration array to the nearest number of seconds.

t = hours(8) + minutes(29:31) + seconds(1.3:0.5:2.3);
t.Format = "hh:mm:ss.SS"
t = 1x3 duration
   08:29:01.30   08:30:01.80   08:31:02.30

Y1 = round(t)
Y1 = 1x3 duration
   08:29:01.00   08:30:02.00   08:31:02.00

Round each value in t to the nearest number of hours.

Y2 = round(t,"hours")
Y2 = 1x3 duration
   08:00:00.00   09:00:00.00   09:00:00.00

Input Arguments

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Input array, specified as a scalar, vector, matrix, or multidimensional array. For complex X, round treats the real and imaginary parts independently.

X must be single or double when you use round with more than one input.

round converts logical and char elements of X into double values.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | char | logical
Complex Number Support: Yes

Number of digits, specified as a scalar integer. When you specify N, the round(X,N) function rounds X to the nearest multiple of 10—N.

If you specify the "significant" rounding type, then N must be a positive integer.

Rounding type, specified as "decimals" or "significant". The rounding type determines whether round considers digits in relation to the decimal point or the overall number of significant digits. N must be a positive integer when you specify "significant". In that case, the round function rounds to the nearest number with N significant digits.

The default value is "decimals", so that round(X,N,"decimals") is equivalent to round(X,N).

Example: round(3132,2,"significant") returns 3100, which is the closest number to 3132 that has 2 significant digits.

Data Types: char | string

Direction to break ties, specified as one of these values:

  • "fromzero" — Round ties away from zero to the nearest integer with larger magnitude.

  • "tozero" — Round ties towards zero to the nearest integer with smaller magnitude.

  • "even" — Round ties to the nearest even integer.

  • "odd" — Round ties to the nearest odd integer.

  • "plusinf" — Round ties towards positive infinity to the nearest integer with larger value.

  • "minusinf" — Round ties towards negative infinity to the nearest integer with smaller value.

Ties are rare. When using round(X,N,TieBreaker=direction), a tie occurs only when X * 10N is within roundoff error of a point halfway between two consecutive integers, that is, X * 10N has a fractional part of 0.5 (within roundoff error) in decimal.

Example: round(2.015,2,TieBreaker="even")

Input duration, specified as a duration array.

Unit of time, specified as "seconds", "minutes", "hours", "days", or "years". A duration of 1 year is equal to exactly 365.2425 24-hour days.

Data Types: char | string

Tips

  • format short and format long both display rounded numbers. This display can cause unexpected results when combined with the round function.

  • For display purposes, use sprintf to control the exact display of a number as a string. For example, to display exactly 2 decimal digits of pi (and no trailing zeros), use sprintf("%.2f",pi).

Extended Capabilities

Version History

Introduced before R2006a

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