# CenteredInterval

CenteredInterval[x,dx]

for real numbers x and dx gives a centered interval that contains the real interval .

CenteredInterval[x+ y,dx+ dy]

gives a centered interval that contains the complex rectangle .

for an approximate number c gives a centered interval that contains all values within the error bounds of c.

# Details  • Centered intervals are also known as center-radius or mid-radius intervals.
• CenteredInterval is typically used to obtain verified bounds on errors accumulated through numeric computation. Given error bounds for all arguments of a function, centered interval computation provides a reliable bound for the error in the function value.
• • gives a centered interval object Δ with the center and the radius , where and are Gaussian rational numbers with power of two denominators. If and are real, then Δ represents the real interval , otherwise Δ represents the complex rectangle .
• Arithmetic operations and many mathematical functions work with centered interval arguments. f[Δ1,,Δn] yields a centered interval object Δ which contains f[a1,,an] for any aiΔi.
• IntervalMemberQ can be used to decide interval membership or inclusion between intervals.
• Relational operators such as Equal and Less yield explicit True or False results whenever they are given disjoint intervals.
• • In StandardForm and related formats, CenteredInterval objects are printed in elided form, with only approximate values of the center and the radius displayed.
• Normal converts CenteredInterval objects to arbitrary-precision numbers with accuracy corresponding to the radius.
• Information[CenteredInterval[], prop] gives the property prop of the center-radius interval. The following properties can be specified:
•  "Center" the center of the interval "Radius" the radius of the interval "Bounds" bounds on the values in the interval

# Examples

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## Basic Examples(3)

Construct a real interval:

Evaluate a function at the interval:

Convert the result to an arbitrary-precision number:

Construct a complex interval:

Evaluate a function at the interval:

Extract the exact values of the center and the radius:

Compute bounds on values of on the rectangle :

Approximate the set of values of on the rectangle :

The computed region lies within the bounds:

## Scope(17)

### Constructing Center-Radius Intervals(7)

Construct a real interval by specifying a center and a radius:

Construct a complex interval by specifying a center and a radius:

Construct centered intervals by specifying arbitrary-precision numbers:

Convert a bounded Interval object to a centered interval:

Binary Gaussian rationals are exactly representable as intervals with radius zero:

Other exact numbers are converted to intervals with nonzero radii:

Nonzero machine-precision numbers are treated as numbers with \$MachinePrecision precise digits:

Convert machine-precision zero to a center-radius interval:

### Interval Arithmetic(5)

Use arithmetic operations with centered interval arguments:

Use centered intervals as arguments of mathematical functions:

Operations with centered interval and numeric arguments yield centered intervals:

The returned interval contains all values of the function in the input interval:

Interval arithmetic operations return Indeterminate if the set of values is unbounded: ### Interval Properties(5)

Extract the properties of a real interval:

The center and the radius are binary rational numbers:

Find rational bounds for the elements of the interval:

Convert the interval to an arbitrary-precision number:

Extract the center and the radius of a complex interval:

The center and the radius are binary Gaussian rational numbers:

Find Gaussian rational bounds for the elements of the interval:

Convert the interval to an arbitrary-precision number:

Test interval membership:

Test inclusion of intervals:

Visualize the intervals:

Compare real intervals:

If the intervals intersect, the comparison cannot be resolved:

Use IntervalIntersection to compute the intersection:

The empty interval is expressed as Interval[]:

## Properties & Relations(2)

Interval arithmetic provides verified bounds on the computation error:

Since , the error for is bounded by :

Arbitrary-precision number arithmetic estimates the error based on the linear term, getting :

Interval represents real intervals given by specifying their endpoints:

Convert the interval to CenteredInterval representation:

Convert it back:

When interval endpoints are not binary rationals, conversion makes the interval larger:

## Possible Issues(1)

Only bounded intervals can be represented as CenteredInterval: Interval representation allows unbounded intervals: