46 lines
1.3 KiB
C
46 lines
1.3 KiB
C
#include "./polynominal_interpolation.h"
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/* Divided difference is evaluated for:
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array y stands for f(x)
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array x stands for x
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number i stands for index of evaluated difference (from 0)
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number d stands for order of difference (from 0)
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example: https://shorturl.at/tBCPS */
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double div_diff(double *y, double *x, int i, int d)
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{
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return (y[i] - y[i - 1]) / (x[i] - x[i - d]);
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}
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/* Evaluates divided differences of n values - array of some kind of derivatives with big enough dx
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Example: https://shorturl.at/tBCPS
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Warning: result is evaluated in `double *y` array */
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double *div_diff_es(double *x, double *y, int n)
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{
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for (int i = 1; i < n; i++) // first element remains unchanged
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for (int j = n - 1; j >= i; j--) // evaluate from the end of array, decreacing number of step every repeation
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y[j] = div_diff(y, x, j, i);
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return y;
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}
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/* Prints interpolation polynomial in Newton notation */
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void print_newton_poly(double *f, double *x, int n)
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{
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for (int i = 0; i < n; i++)
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{
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printf("(%lf)", f[i]);
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for (int j = 0; j < i; j++)
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printf("*(x-(%lf))", x[j]);
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if (i != n - 1)
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printf("+");
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}
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}
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int main()
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{
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double x[] = {0, 1, 2, 3},
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y[] = {-2, -5, 0, -4};
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print_newton_poly(div_diff_es(x, y, 4), x, 4);
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} |