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polyinterp Class Reference

Support for four point polynomial interpolation, using the Lagrange formula. More...

#include <polyinterp.h>

List of all members.

Public Methods
	polyinterp ()
	The polyinterp (polynomial interpolation) class constructor calculates the coefficients for a four point polynomial interpolated at -0.5, 0.5, 1.5, 2.5 and 3.5. More...
double	interpPoint (double x, int N, double d[])
	Given four points at the x,y coordinates {0,d0}, {1,d1}, {2,d2}, {3,d3} return the y-coordinate value for the polynomial interpolated point at x. More...
Private Methods
void	lagrange (double x, int N, double c[])
	The polynomial interpolation algorithm assumes that the known points are located at x-coordinates 0, 1,.. More...
void	fillTable (const int N, double table[4][4])
	For a given N-point polynomial interpolation, fill the coefficient table, for points 0.5 ... More...
void	printTable (double table[4][4], int N)
	Print an N x N table polynomial coefficient table. More...
void	printTables ()
	Print the 4-point and 2-point polynomial coefficient tables. More...
void	getCoef (double x, int n, double c[])
	For the polynomial interpolation point x-coordinate x, return the associated polynomial interpolation coefficients. More...
Private Attributes
double	fourPointTable [4][4]
double	twoPointTable [4][4]

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Detailed Description

Support for four point polynomial interpolation, using the Lagrange formula.

Definition at line 32 of file polyinterp.h.

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Constructor & Destructor Documentation

polyinterp::polyinterp ( ) [inline]

The polyinterp (polynomial interpolation) class constructor calculates the coefficients for a four point polynomial interpolated at -0.5, 0.5, 1.5, 2.5 and 3.5. Definition at line 163 of file polyinterp.h. { // Fill in the 4-point polynomial interplation table // for the points 0.5, 1.5, 2.5, 3.5 fillTable( 4, fourPointTable ); // Fill in the 2-point polynomial interpolation table // for 0.5 and 1.5 fillTable( 2, twoPointTable ); } // polyinterp class constructor

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Member Function Documentation

void polyinterp::fillTable ( const int N, double table[4][4] ) [inline, private]

For a given N-point polynomial interpolation, fill the coefficient table, for points 0.5 ... (N-0.5). Definition at line 73 of file polyinterp.h. Referenced by polyinterp(). { double x; double n = N; int i = 0; for (x = 0.5; x < n; x = x + 1.0) { lagrange( x, N, table[i] ); i++; } } // fillTable

void polyinterp::getCoef ( double x, int n, double c[] ) [inline, private]

For the polynomial interpolation point x-coordinate x, return the associated polynomial interpolation coefficients. Parameters: x   the x-coordinate for the interpolated pont n   the number of polynomial interpolation points c   [] an array to return the polynomial coefficients Definition at line 127 of file polyinterp.h. Referenced by interpPoint(). { int j = (int)x; if (j < 0 || j >= n) { printf("poly::getCoef: n = %d, bad x value = %f\n", n, x); } if (n == 2) { c[2] = 0.0; c[3] = 0.0; } else if (n != 4) { printf("poly::getCoef: bad value for N\n"); return; } for (int i = 0; i < n; i++) { if (n == 4) { c[i] = fourPointTable[j][i]; } else { // n == 2 c[i] = twoPointTable[j][i]; } } } // getCoef

double polyinterp::interpPoint ( double x, int N, double d[] ) [inline]

Given four points at the x,y coordinates {0,d0}, {1,d1}, {2,d2}, {3,d3} return the y-coordinate value for the polynomial interpolated point at x. Parameters: x   the x-coordinate for the point to be interpolated N   the number of interpolation points d   [] an array containing the y-coordinate values for the known points (which are located at x-coordinates 0..N-1). Definition at line 187 of file polyinterp.h. Referenced by polyHaar::interp(), and poly::predict(). { double c[4]; double point = 0; int n = 4; if (N < 4) n = N; getCoef( x, n, c ); if (n == 4) { point = c[0]*d[0] + c[1]*d[1] + c[2]*d[2] + c[3]*d[3]; } else if (n == 2) { point = c[0]*d[0] + c[1]*d[1]; } return point; } // interpPoint

void polyinterp::lagrange ( double x, int N, double c[] ) [inline, private]

The polynomial interpolation algorithm assumes that the known points are located at x-coordinates 0, 1,.. N-1. An interpolated point is calculated at x, using N coefficients. The polynomial coefficients for the point x can be calculated staticly, using the Lagrange method. Parameters: x   the x-coordinate of the interpolated point N   the number of polynomial points. c   [] an array for returning the coefficients Definition at line 50 of file polyinterp.h. Referenced by fillTable(). { double num, denom; for (int i = 0; i < N; i++) { num = 1; denom = 1; for (int k = 0; k < N; k++) { if (i != k) { num = num * (x - k); denom = denom * (i - k); } } // for k c[i] = num / denom; } // for i } // lagrange

void polyinterp::printTable ( double table[4][4], int N ) [inline, private]

Print an N x N table polynomial coefficient table. Definition at line 89 of file polyinterp.h. Referenced by printTables(). { printf("%d-point interpolation table:\n", N); double x = 0.5; for (int i = 0; i < N; i++) { printf("%4.2f: ", x); for (int j = 0; j < N; j++) { printf("%6.4f", table[i][j] ); if (j < N-1) printf(", "); } printf("\n"); x = x + 1.0; } }

void polyinterp::printTables ( ) [inline, private]

Print the 4-point and 2-point polynomial coefficient tables. Definition at line 110 of file polyinterp.h. { printTable( fourPointTable, 4 ); printTable( twoPointTable, 2 ); printf("\n"); } // printTables

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Member Data Documentation

double polyinterp::fourPointTable [private]

Definition at line 35 of file polyinterp.h.

double polyinterp::twoPointTable [private]

Definition at line 36 of file polyinterp.h.

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The documentation for this class was generated from the following file:

• polyinterp.h

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