2 * We try to find an optimal triangle grid
9 #include <gsl/gsl_errno.h>
10 #include <gsl/gsl_multimin.h>
12 static const char *input_file, *output_file;
13 static char *output_file_tmp;
15 static double edgewise_vertex_displacement_cost(const Vertices vertices);
16 static double noncircular_rim_cost(const Vertices vertices);
18 static void compute_vertex_areas(const Vertices vertices, double areas[N]);
19 static double best_energy= DBL_MAX;
21 static void addcost(double *energy, double tweight, double tcost);
22 #define COST(weight, compute) addcost(&energy, (weight), (compute))
24 /*---------- main energy computation and subroutines ----------*/
26 static double compute_energy(const Vertices vertices) {
27 double vertex_areas[N], energy;
29 compute_vertex_areas(vertices,vertex_areas);
31 printf("cost > energy |");
33 COST(1e4, edgewise_vertex_displacement_cost(vertices));
34 COST(1e2, graph_layout_cost(vertices,vertex_areas));
35 COST(1e4, noncircular_rim_cost(vertices));
37 printf("| total %# e |", energy);
38 if (energy < best_energy) {
44 best_f= fopen(output_file_tmp,"wb"); if (!best_f) diee("fopen new out");
45 r= fwrite(vertices,sizeof(Vertices),1,best_f); if (r!=1) diee("fwrite");
46 if (fclose(best_f)) diee("fclose new best");
47 if (rename(output_file_tmp,output_file)) diee("rename install new best");
57 static void addcost(double *energy, double tweight, double tcost) {
58 double tenergy= tweight * tcost;
59 printf(" %# e > %# e |", tcost, tenergy);
63 static void compute_vertex_areas(const Vertices vertices, double areas[N]) {
64 int v0,v1,v2, e1,e2, k;
75 double e1v[D3], e2v[D3], av[D3];
77 e1v[k]= vertices[v1][k] - vertices[v0][k];
78 e2v[k]= vertices[v2][k] - vertices[v0][k];
84 areas[v0]= total / count;
88 /*---------- use of GSL ----------*/
90 /* We want to do multidimensional minimisation.
92 * We don't think there are any local minima. Or at least, if there
93 * are, the local minimum which will be found from the starting
94 * state is the one we want.
96 * We don't want to try to provide a derivative of the cost
97 * function. That's too tedious (and anyway the polynomial
98 * approximation to our our cost function sometimes has high degree
99 * in the inputs which means the quadratic model implied by most of
100 * the gradient descent minimisers is not ideal).
102 * This eliminates most of the algorithms. Nelder and Mead's
103 * simplex algorithm is still available and we will try that.
105 * In our application we are searching for the optimal locations of
106 * N actualvertices in D3 (3) dimensions - ie, we are searching for
107 * the optimal metapoint in an N*D3-dimensional space.
109 * So eg with X=Y=100, the simplex will contain 300 metavertices
110 * each of which is an array of 300 doubles for the actualvertex
111 * coordinates. Hopefully this won't be too slow ...
114 static gsl_multimin_fminimizer *minimiser;
116 static const double stop_epsilon= 1e-4;
118 static double minfunc_f(const gsl_vector *x, void *params) {
119 assert(x->size == DIM);
120 assert(x->stride == 1);
121 return compute_energy((const double(*)[D3])x->data);
124 int main(int argc, const char *const *argv) {
125 gsl_multimin_function multimin_function;
127 Vertices initial, step_size;
129 gsl_vector initial_gsl, step_size_gsl;
132 if (argc!=3 || argv[1][0]=='-' || strncmp(argv[2],"-o",2))
133 { fputs("usage: minimise <input> -o<output\n",stderr); exit(8); }
136 output_file= argv[2]+2;
137 if (asprintf(&output_file_tmp,"%s.new",output_file) <= 0) diee("asprintf");
139 minimiser= gsl_multimin_fminimizer_alloc
140 (gsl_multimin_fminimizer_nmsimplex, DIM);
141 if (!minimiser) { perror("alloc minimiser"); exit(-1); }
143 multimin_function.f= minfunc_f;
144 multimin_function.n= DIM;
145 multimin_function.params= 0;
147 initial_f= fopen(input_file,"rb"); if (!initial_f) diee("fopen initial");
148 errno= 0; r= fread(initial,sizeof(initial),1,initial_f);
149 if (r!=1) diee("fread");
152 initial_gsl.size= DIM;
153 initial_gsl.stride= 1;
154 initial_gsl.block= 0;
155 initial_gsl.owner= 0;
156 step_size_gsl= initial_gsl;
158 initial_gsl.data= &initial[0][0];
159 step_size_gsl.data= &step_size[0][0];
162 K step_size[v][k]= 0.03;
164 // FOR_RIM_VERTEX(vx,vy,v)
165 // step_size[v][3] *= 0.1;
167 GA( gsl_multimin_fminimizer_set(minimiser, &multimin_function,
168 &initial_gsl, &step_size_gsl) );
171 GA( gsl_multimin_fminimizer_iterate(minimiser) );
173 size= gsl_multimin_fminimizer_size(minimiser);
174 r= gsl_multimin_test_size(size, stop_epsilon);
176 printf("%*s size %# e, r=%d\n", 135,"", size, r);
179 if (r==GSL_SUCCESS) break;
180 assert(r==GSL_CONTINUE);
185 /*---------- Edgewise vertex displacement ----------*/
205 * Find R', the `expected' location of R, by
206 * reflecting S in M (the midpoint of QP).
212 * Giving energy contribution:
220 * (The dimensions of this are those of F_vd.)
222 * By symmetry, this calculation gives the same answer with R and S
223 * exchanged. Looking at the projection in the RMS plane:
229 * R' ,' 2d" = |SS'| = |RR'| = 2d
231 * `-._ ,' By congruent triangles,
232 * ` M with M' = midpoint of RS,
233 * ,' `-._ |MM'| = |RR'|/2 = d
236 * ,' M' _ , - ' d = |MM'|
240 * We choose this value for l (rather than |RM|+|MS|, say, or |RM|)
241 * because we want this symmetry and because we're happy to punish
242 * bending more than uneveness in the metric.
244 * In practice to avoid division by zero we'll add epsilon to l^3
245 * and the huge energy ought then to be sufficient for the model to
246 * avoid being close to R=S.
249 static double edgewise_vertex_displacement_cost(const Vertices vertices) {
250 static const double l3_epsilon= 1e-6;
252 int pi,e,qi,ri,si, k;
253 double m[D3], mprime[D3], b, d2, l, sigma_bd2_l3=0;
256 ri= EDGE_END2(pi,(e+1)%V6); if (ri<0) continue;
257 si= EDGE_END2(pi,(e+5)%V6); if (si<0) continue;
259 K m[k]= (vertices[pi][k] + vertices[qi][k]) * 0.5;
260 K mprime[k]= (vertices[ri][k] + vertices[si][k]) * 0.5;
261 b= hypotD(vertices[pi], vertices[qi]);
262 d2= hypotD2(m, mprime);
263 l= hypotD(vertices[ri], vertices[si]);
264 double l3 = l*l*l + l3_epsilon;
266 sigma_bd2_l3 += b * d2 / l3;
271 /*---------- noncircular rim cost ----------*/
273 static double noncircular_rim_cost(const Vertices vertices) {
277 FOR_RIM_VERTEX(vy,vx,v) {
279 /* By symmetry, nearest point on circle is the one with
280 * the same angle subtended at the z axis. */
281 oncircle[0]= vertices[v][0];
282 oncircle[1]= vertices[v][1];
284 double mult= 1.0/ magnD(oncircle);
287 double d2= hypotD2(vertices[v], oncircle);