--- Phil Steitz <[EMAIL PROTECTED]> wrote:I actually intended to make this public, but read-only and using copy semantics. Any client should have (read-only) access to this basic property of the Polynomial, IMHO.
0. To help debug the SplineInterpolater (PR #28019 et al), I need to expose the coefficients in o.a.c.m.analysis.Polynomial as a read-only property (returning an array copy). Any objections to adding this?
+1 if you do it by adding a package-level-accessible (i.e., no access modifier keyword; the JUnit test would be able to access it by being in the same package) getter method -- which sounds like what you're proposing.
Phil
While reviewing the code, I also noticed that the current impl uses "naive" evaluation (using Math.pow, etc.). I would like to change this to use Horner's Method. Here is what I have ready to commit:
1. Add protected static double evaluate(double[] coefficients, double argument) implementing Horner to get the function value; and change value(double) to just call this.
2. Add protected static double[] differentiate(double[] coefficients) to return the coefficients of the derivative of the polynomial with coefficients equal to the actual parameter. Then change firstDerivative(x) to just return
evaluate(differentiate(coefficients), x). Similar for secondDerivative.
I could adapt Horner for the derivatives, but that seems messy to me and the slight memory cost to create the temp arrays seems worth it.
3. I would also like to add public PolynomialFunction derivative() { return new PolynomialFunction(differentiate(coefficients)); }
Any objections to this?
+1, these sound reasonable.
Interestingly, while Horner's method should give better numerics, it actually fails to get within 1E-15 for one of the quintic test cases, performing worse than the "naive" impl. The error is in the 16th significant digit, which is not surprising. I would like to change the tolerance to 1E-12 (current tests actually succeed at 1E-14).
Phil
I wonder why that is? Does Math.pow() use higher-than-double precision and then cast down to double? I think we should consider carefully what is implied by the fact that Horner's method has worse precision. Also, I would in principle like to leave the tolerance as tight as possible, 1E-14 in this case.
Al
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