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#include <algorithm>
#include <cassert>
#include <cstdlib>
#include <iostream>
#include <vector>
using namespace std;
#include "vecmathlib.h"
using namespace vecmathlib;
typedef float64_vec realvec_t;
typedef realvec_t::real_t real_t;
typedef realvec_t::intvec_t intvec_t;
typedef intvec_t::int_t int_t;
realvec_t interp(const real_t* array, ptrdiff_t size,
real_t xmin, real_t xmax,
realvec_t x)
{
assert(size >= 2);
// spacing
real_t dx = (xmax - xmin) / (size - 1);
real_t idx = 1.0 / dx;
// determine location in array
realvec_t scaled = (x - realvec_t(xmin)) * realvec_t(idx);
realvec_t cell = floor(scaled);
intvec_t n = convert_int(cell);
// gather values from array
realvec_t x0, x1;
for (ptrdiff_t i=0; i<realvec_t::size; ++i) {
// ensure location is not out of bounds
ptrdiff_t j = max(ptrdiff_t(0), min(size-2, ptrdiff_t(n[i])));
x0.set_elt(i, array[j]);
x1.set_elt(i, array[j+1]);
}
// determine interpolation weights
realvec_t offset = scaled - cell;
realvec_t w0 = realvec_t(1.0) - offset;
realvec_t w1 = offset;
// interpolate
realvec_t y = w0 * x0 + w1 * x1;
return y;
}
int main(int argc, char** argv)
{
ptrdiff_t size = 1001;
vector<real_t> array(size);
for (ptrdiff_t i=0; i<size; ++i) array[i] = real_t(i) / 1000.0;
real_t xmin = 0.0;
real_t xmax = 0.5;
realvec_t x = 0.333;
cout << "x=" << x << "\n";
realvec_t y = interp(&array[0], size, xmin, xmax, x);
cout << "y=" << y << "\n";
return 0;
}
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