47 lines
2.9 KiB
C
47 lines
2.9 KiB
C
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "dsp/core/core.h"
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#include "libc/math.h"
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#include "libc/str/str.h"
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/**
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* Computes 𝐀⁻¹ inverted 3×3 matrix, if it exists.
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*
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* @param 𝐁 is destination memory
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* @param 𝐀 is input matrix, which can't overlap 𝐁
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* @param 𝑑 is |𝐀| the determinant scalar or 0 if degenerate
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* @return 𝐀⁻¹ stored inside 𝐁 or NaNs if 𝑑=0
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* @define 𝐀⁻¹=𝐁 such that 𝐀×𝐁=𝐁×𝐀=𝐈ₙ
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* @see det3()
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*/
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void *inv3(double B[restrict 3][3], const double A[restrict 3][3], double d) {
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d = d ? 1 / d : NAN;
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B[0][0] = (A[1][1] * A[2][2] - A[2][1] * A[1][2]) * d;
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B[0][1] = (A[2][1] * A[0][2] - A[0][1] * A[2][2]) * d;
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B[0][2] = (A[0][1] * A[1][2] - A[1][1] * A[0][2]) * d;
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B[1][0] = (A[2][0] * A[1][2] - A[1][0] * A[2][2]) * d;
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B[1][1] = (A[0][0] * A[2][2] - A[2][0] * A[0][2]) * d;
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B[1][2] = (A[1][0] * A[0][2] - A[0][0] * A[1][2]) * d;
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B[2][0] = (A[1][0] * A[2][1] - A[2][0] * A[1][1]) * d;
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B[2][1] = (A[2][0] * A[0][1] - A[0][0] * A[2][1]) * d;
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B[2][2] = (A[0][0] * A[1][1] - A[1][0] * A[0][1]) * d;
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return B;
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}
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