```/* nag_mesh_dim2_gen_front (d06acc) Example Program.
*
* Copyright 2020 Numerical Algorithms Group.
*
* Mark 27.1, 2020.
*/

#include <math.h>
#include <nag.h>
#include <stdio.h>

/* Structure to allow data to be passed onto */
/* the nag_mesh_dim2_gen_boundary (d06bac) user-supplied function fbnd */

struct user {
/* details of the double NACA0012 and the circle around it */

double x0, y0, x1, y1, radius;
};

#ifdef __cplusplus
extern "C" {
#endif
static double NAG_CALL fbnd(Integer, double, double, Nag_Comm *);
#ifdef __cplusplus
}
#endif

#define EDGE(I, J) edge[3 * ((J)-1) + (I)-1]
#define LINED(I, J) lined[4 * ((J)-1) + (I)-1]
#define CONN(I, J) conn[3 * ((J)-1) + (I)-1]
#define COOR(I, J) coor[2 * ((J)-1) + (I)-1]
#define COORCH(I, J) coorch[2 * ((J)-1) + (I)-1]

int main(void) {
const Integer nus = 1, nvmax = 2000, nedmx = 200, nvint = 40;
struct user geom_Naca;
double dnvint, radius, x0, x1, y0, y1;
Integer exit_status = 0, i, itrace, j, k, l, ncomp, nedge, nelt, nlines;
Integer nv, nvb, nvint2, reftk;
char pmesh[2];
double *coor = 0, *coorch = 0, *coorus = 0, *rate = 0, *weight = 0;
Integer *conn = 0, *edge = 0, *lcomp = 0, *lined = 0, *nlcomp = 0;
NagError fail;
Nag_Comm comm;

INIT_FAIL(fail);

printf(" nag_mesh_dim2_gen_front (d06acc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");

/* Initialize boundary mesh inputs: the number of lines and */
/* the number of characteristic points of the boundary mesh */
scanf("%" NAG_IFMT "", &nlines);
scanf("%*[^\n] ");

/* Allocate memory */

if (!(coor = NAG_ALLOC(2 * nvmax, double)) ||
!(coorch = NAG_ALLOC(2 * nlines, double)) ||
!(coorus = NAG_ALLOC(2 * nus, double)) ||
!(rate = NAG_ALLOC(nlines, double)) ||
!(weight = NAG_ALLOC(nvint, double)) ||
!(conn = NAG_ALLOC(3 * (2 * nvmax + 5), Integer)) ||
!(edge = NAG_ALLOC(3 * nedmx, Integer)) ||
!(lined = NAG_ALLOC(4 * nlines, Integer)) ||
!(lcomp = NAG_ALLOC(nlines, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* The double NACA0012 and the circle around it */
for (j = 1; j <= nlines; ++j)
scanf("%lf", &COORCH(1, j));
scanf("%*[^\n] ");
for (j = 1; j <= nlines; ++j)
scanf("%lf", &COORCH(2, j));
scanf("%*[^\n] ");

/* The lines of the boundary mesh */

for (j = 1; j <= nlines; ++j) {
for (i = 1; i <= 4; ++i)
scanf("%" NAG_IFMT "", &LINED(i, j));
scanf("%lf", &rate[j - 1]);
}
scanf("%*[^\n] ");

/* The number of connected components to */
/* the boundary and their information */
scanf("%" NAG_IFMT "", &ncomp);
scanf("%*[^\n] ");

/* Allocate memory */

if (!(nlcomp = NAG_ALLOC(ncomp, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

j = 0;
for (i = 0; i < ncomp; ++i) {
scanf("%" NAG_IFMT "", &nlcomp[i]);
scanf("%*[^\n] ");
l = j + NAG_IABS(nlcomp[i]);
for (k = j; k < l; ++k)
scanf("%" NAG_IFMT "", &lcomp[k]);
scanf("%*[^\n] ");

j += NAG_IABS(nlcomp[i]);
}
scanf(" ' %1s '%*[^\n]", pmesh);

/* Data passed to the user-supplied function */

x0 = 1.5;
y0 = 0.0;
x1 = 0.8;
y1 = -0.3;

comm.p = (Pointer)&geom_Naca;

geom_Naca.x0 = x0;
geom_Naca.y0 = y0;
geom_Naca.x1 = x1;
geom_Naca.y1 = y1;

itrace = 0;

/* Call to the 2D boundary mesh generator */

/* nag_mesh_dim2_gen_boundary (d06bac).
* Generates a boundary mesh
*/
nag_mesh_dim2_gen_boundary(nlines, coorch, lined, fbnd, coorus, nus, rate,
ncomp, nlcomp, lcomp, nvmax, nedmx, &nvb, coor,
&nedge, edge, itrace, 0, &comm, &fail);

if (fail.code == NE_NOERROR) {
if (pmesh[0] == 'N') {
printf(" Boundary mesh characteristics\n");
printf(" nvb   =%6" NAG_IFMT "\n", nvb);
printf(" nedge =%6" NAG_IFMT "\n", nedge);
} else if (pmesh[0] == 'Y') {
/* Output the mesh to view it using the NAG Graphics Library */

printf(" %10" NAG_IFMT " %10" NAG_IFMT "\n", nvb, nedge);

for (i = 1; i <= nvb; ++i)
printf("  %4" NAG_IFMT "  %15.6e  %15.6e  \n", i, COOR(1, i),
COOR(2, i));

for (i = 1; i <= nedge; ++i)
printf(" %4" NAG_IFMT " %4" NAG_IFMT " %4" NAG_IFMT " %4" NAG_IFMT "\n",
i, EDGE(1, i), EDGE(2, i), EDGE(3, i));
} else {
printf("Problem with the printing option Y or N\n");
exit_status = -1;
goto END;
}
} else {
printf("Error from nag_mesh_dim2_gen_boundary (d06bac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Initialize mesh control parameters */

itrace = 0;

/* Generation of interior vertices */
/* for the wake of the first NACA */

nvint2 = nvint / 2;
dnvint = 5.0 / (nvint2 + 1.0);

for (i = 1; i <= nvint2; ++i) {
reftk = nvb + i;
COOR(1, reftk) = i * dnvint + 1.0;
COOR(2, reftk) = 0.0;
weight[i - 1] = 0.05;
}

/* for the wake of the second one */

dnvint = 4.19 / (nvint2 + 1.0);

for (i = nvint2 + 1; i <= nvint; ++i) {
reftk = nvb + i;
COOR(1, reftk) = (i - nvint2) * dnvint + 1.8;
COOR(2, reftk) = -0.3;
weight[i - 1] = 0.05;
}

/* Call to the 2D Advancing front mesh generator */

/* nag_mesh_dim2_gen_front (d06acc).
* Generates a two-dimensional mesh using an Advancing-front
* method
*/
nag_mesh_dim2_gen_front(nvb, nvint, nvmax, nedge, edge, &nv, &nelt, coor,
conn, weight, itrace, 0, &fail);

if (fail.code == NE_NOERROR) {
if (pmesh[0] == 'N') {
printf(" Complete mesh characteristics\n");
printf("   nv (rounded to nearest 10) =%6" NAG_IFMT "\n",
10 * ((nv + 5) / 10));
printf(" nelt (rounded to nearest 10) =%6" NAG_IFMT "\n",
10 * ((nelt + 5) / 10));
} else if (pmesh[0] == 'Y') {
/* Output the mesh to view it using the NAG Graphics Library */

printf(" %10" NAG_IFMT " %10" NAG_IFMT "\n", nv, nelt);

for (i = 1; i <= nv; ++i)
printf("  %15.6e  %15.6e\n", COOR(1, i), COOR(2, i));

reftk = 0;
for (k = 1; k <= nelt; ++k)
printf(" %10" NAG_IFMT "%10" NAG_IFMT "%10" NAG_IFMT "%10" NAG_IFMT
"\n",
CONN(1, k), CONN(2, k), CONN(3, k), reftk);
} else {
printf("Problem with the printing option Y or N\n");
exit_status = -1;
goto END;
}
} else {
printf("Error from nag_mesh_dim2_gen_front (d06acc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

END:
NAG_FREE(coor);
NAG_FREE(coorch);
NAG_FREE(coorus);
NAG_FREE(rate);
NAG_FREE(weight);
NAG_FREE(conn);
NAG_FREE(edge);
NAG_FREE(lcomp);
NAG_FREE(lined);
NAG_FREE(nlcomp);

return exit_status;
}

double NAG_CALL fbnd(Integer i, double x, double y, Nag_Comm *pcomm) {
double ret_val;
double c, radius, x0, x1, y0, y1;
struct user *geom_Naca = (struct user *)pcomm->p;

x0 = geom_Naca->x0;
y0 = geom_Naca->y0;
x1 = geom_Naca->x1;
y1 = geom_Naca->y1;

ret_val = 0.0;

switch (i) {
case 1:

/* upper NACA0012 wing beginning at the origin */

c = 1.008930411365;

ret_val = 0.6 * (0.2969 * sqrt(c * x) - 0.126 * (c * x) -
0.3516 * pow(c * x, 2.0) + 0.2843 * pow(c * x, 3.0) -
0.1015 * pow(c * x, 4.0)) -
c * y;
break;

case 2:

/* lower NACA0012 wing beginning at the origin */

c = 1.008930411365;

ret_val = 0.6 * (0.2969 * sqrt(c * x) - 0.126 * (c * x) -
0.3516 * pow(c * x, 2.0) + 0.2843 * pow(c * x, 3.0) -
0.1015 * pow(c * x, 4.0)) +
c * y;

break;

case 3:

/* the circle around the double NACA */

ret_val = (x - x0) * (x - x0) + (y - y0) * (y - y0) - radius * radius;
break;

case 4:

/* upper NACA0012 wing beginning at (X1;Y1) */

c = 1.008930411365;

ret_val = 0.6 * (0.2969 * sqrt(c * (x - x1)) - 0.126 * c * (x - x1) -
0.3516 * pow(c * (x - x1), 2.0) +
0.2843 * pow(c * (x - x1), 3.0) -
0.1015 * pow(c * (x - x1), 4.0)) -
c * (y - y1);
break;

case 5:

/* lower NACA0012 wing beginning at (X1;Y1) */

c = 1.008930411365;

ret_val = 0.6 * (0.2969 * sqrt(c * (x - x1)) - 0.126 * (c * (x - x1)) -
0.3516 * pow(c * (x - x1), 2.0) +
0.2843 * pow(c * (x - x1), 3.0) -
0.1015 * pow(c * (x - x1), 4.0)) +
c * (y - y1);
break;
}

return ret_val;
}
```