# Example 5 -- interpolated closed parametric curves and derivatives

```#include <stdio.h>
#include <ncarg/ngmath.h>

/*
* This example shows how to use the double precision C routines in
* Fitgrid. In order to plot this double precision data using NCAR
* Graphics, you must link with a double precision version of NCAR
* Graphics.
*/

/*
*  Example of c_ftkurvpdp and c_ftkurvpddp.
*/

#define IDIM  11
#define IOUT 201

main()
{
double x[] = { 13.0,  9.0,  9.0, 16.0, 21.0, 27.0,
34.0, 36.0, 34.0, 26.0, 19.5       };
double y[] = { 35.0, 31.0, 18.0, 12.0,  9.6,  8.4,
13.2, 21.6, 30.0, 37.2, 37.4       };
double xinc, xo[IOUT], yo[IOUT], xs[IOUT], ys[IOUT],
xd[IOUT], yd[IOUT], xdd[IOUT], ydd[IOUT],
xp[IDIM], yp[IDIM], u[IOUT];
double tinc;
int   i;

/*
*  Set up the array of parameter values where we want to obtain
*  interpolated values.
*/
tinc = 1./(IOUT-1.);
for (i = 0; i < IOUT; i++) {
u[i] = tinc * (double) i;
}

/*
*  Get the interpolated points.
*/
c_ftkurvpdp(IDIM, x, y, IOUT, u, xo, yo);

/*
*  Get the derivatives (this returns the interpolsted values as well).
*/
c_ftkurvpddp(IDIM, x, y, IOUT, u, xs, ys, xd, yd, xdd, ydd);
}

```

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