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56 lines
1.2 KiB
C++
56 lines
1.2 KiB
C++
/*
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Some spline algorithms
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Copyright 2018 Ahmet Inan <inan@aicodix.de>
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*/
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#pragma once
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namespace DSP {
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template <int KNOTS, typename OTYPE, typename ITYPE>
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class UniformNaturalCubicSpline
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{
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OTYPE A[KNOTS-1], B[KNOTS-1], C[KNOTS-1], D[KNOTS-1];
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ITYPE x0, dx;
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public:
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UniformNaturalCubicSpline() = default;
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UniformNaturalCubicSpline(OTYPE *y, ITYPE x0 = 0, ITYPE dx = 1, int STRIDE = 1) : x0(x0), dx(dx)
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{
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ITYPE u[KNOTS-1];
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u[0] = ITYPE(0);
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OTYPE z[KNOTS-1];
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z[0] = ITYPE(0);
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for (int i = 1; i < KNOTS - 1; ++i) {
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ITYPE l = ITYPE(4) - u[i-1];
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u[i] = ITYPE(1) / l;
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z[i] = (ITYPE(3) * (y[(i+1)*STRIDE] - ITYPE(2) * y[i*STRIDE] + y[(i-1)*STRIDE]) - z[i-1]) / l;
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}
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OTYPE c(ITYPE(0));
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for (int i = KNOTS - 2; i >= 0; --i) {
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A[i] = y[i * STRIDE];
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C[i] = z[i] - u[i] * c;
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B[i] = y[(i+1)*STRIDE] - y[i*STRIDE] - (c + ITYPE(2) * C[i]) / ITYPE(3);
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D[i] = (c - C[i]) / ITYPE(3);
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c = C[i];
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}
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}
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OTYPE operator () (ITYPE x)
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{
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ITYPE tx = (x - x0) / dx;
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int k = tx;
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ITYPE t = tx - ITYPE(k);
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if (k < 0) {
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t = tx;
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k = 0;
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}
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if (k >= KNOTS - 1) {
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t = tx - ITYPE(KNOTS-2);
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k = KNOTS-2;
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}
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return A[k] + t * (B[k] + t * (C[k] + t * D[k]));
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}
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};
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}
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