EvaluatePolynomial - Maple Help
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RealBox

  

EvaluatePolynomial

  

evaluate a univariate polynomial at a RealBox object

 

Calling Sequence

Parameters

Description

Examples

Compatibility

Calling Sequence

EvaluatePolynomial(a, [c0, c1, ..., cn])

EvaluatePolynomial(a, [c0, c1, ..., cn], precopt)

Parameters

a

-

a RealBox object

c0, c1, ..., cn

-

real constants or RealBox objects

precopt

-

(optional) equation of the form precision = n, where n is a positive integer

Description

• 

The EvaluatePolynomial command evaluates a dense univariate polynomial at a RealBox object. It does this in a manner that sometimes produces a smaller radius than simple evaluation using the standard arithmetic operations.

• 

The first argument is a RealBox object, representing the value at which the polynomial is to be evaluated.

• 

The second argument is a list of n+1 coefficients of the polynomial to be evaluated, where n is the degree of the polynomial. The first entry is the constant coefficient, the second the linear coefficient, and so on. Each coefficient can be a RealBox object or a real constant.

Examples

Consider the polynomial 49⁢x4−188⁢x2+72⁢x+292. Evaluate it at the RealBox object with center −1.47 and radius 0.01. We first use simple evaluation using the regular arithmetic operators.

> 

poly≔292+72⁢x−188⁢x2+49⁢x4

poly≔49⁢x4−188⁢x2+72⁢x+292

(1)
> 

rb≔RealBox⁡−1.47,0.01

rb≔⟨RealBox: -1.47±0.01⟩

(2)
> 

eval⁡poly,x=rb

⟨RealBox: 8.71575±12.5558⟩

(3)

The radius of the result is smaller if we first convert the polynomial to Horner form.

> 

poly_horner≔convert⁡poly,horner

poly_horner≔292+72+49⁢x2−188⁢x⁢x

(4)
> 

eval⁡poly_horner,x=rb

⟨RealBox: 8.71575±6.30864⟩

(5)

However, this is still a severe overestimation of the radius: the minimal value on this interval is about 8.713 and the maximal value of about 8.781 is achieved at x=−1.46. We verify these values numerically and graphically below.

> 

plot⁡poly,x=−1.48..−1.46

> 

Optimization:-Minimize⁡poly,x=−1.48..−1.46

8.71324004901427,x=−1.47236599608282

(6)
> 

eval⁡poly,x=−1.46

8.7814094

(7)

So ideally we would like the result to have a center of about  8.747 and a radius of about 0.034. We don't quite achieve that with EvaluatePolynomial, but we get much closer than with the other options above.

> 

EvaluatePolynomial⁡rb,PolynomialTools:-CoefficientList⁡poly,x

⟨RealBox: 8.71575±0.0662341⟩

(8)

Compatibility

• 

The RealBox:-EvaluatePolynomial command was introduced in Maple 2023.

• 

For more information on Maple 2023 changes, see Updates in Maple 2023.

See Also

ComplexBox:-EvaluatePolynomial