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32 lines
826 B
32 lines
826 B
4 months ago
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// polynomial for approximating cos(x)
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//
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// Copyright (c) 2019, Arm Limited.
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// SPDX-License-Identifier: MIT
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deg = 8; // polynomial degree
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a = -pi/4; // interval
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b = pi/4;
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// find even polynomial with minimal abs error compared to cos(x)
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f = cos(x);
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// return p that minimizes |f(x) - poly(x) - x^d*p(x)|
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approx = proc(poly,d) {
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return remez(f(x)-poly(x), deg-d, [a;b], x^d, 1e-10);
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};
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// first coeff is fixed, iteratively find optimal double prec coeffs
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poly = 1;
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for i from 1 to deg/2 do {
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p = roundcoefficients(approx(poly,2*i), [|D ...|]);
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poly = poly + x^(2*i)*coeff(p,0);
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};
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display = hexadecimal;
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print("rel error:", accurateinfnorm(1-poly(x)/f(x), [a;b], 30));
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print("abs error:", accurateinfnorm(f(x)-poly(x), [a;b], 30));
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print("in [",a,b,"]");
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print("coeffs:");
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for i from 0 to deg do coeff(poly,i);
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