EXODUS/packages/seacas/libraries/chaco/inertial/inertial2d.c

/*
 * Copyright(C) 1999-2020, 2022, 2023 National Technology & Engineering Solutions
 * of Sandia, LLC (NTESS).  Under the terms of Contract DE-NA0003525 with
 * NTESS, the U.S. Government retains certain rights in this software.
 *
 * See packages/seacas/LICENSE for details
 */

#include "defs.h"    // for TRUE
#include "smalloc.h" // for sfree, smalloc
#include "structs.h" // for vtx_data
#include <stdio.h>   // for printf

void inertial2d(struct vtx_data **graph,        /* graph data structure for weights */
                int               nvtxs,        /* number of vtxs in graph */
                int               cube_or_mesh, /* 0 => hypercube, d => d-dimensional mesh */
                int               nsets,        /* number of sets to divide into */
                float *x, float *y,             /* x and y coordinates of vertices */
                int    *sets,                   /* set each vertex gets assigned to */
                double *goal,                   /* desired set sizes */
                int     using_vwgts             /* are vertex weights being used? */
)
{
  extern int    DEBUG_INERTIAL;     /* debug flag for inertial method */
  extern double inertial_axis_time; /* time spent finding inertial axis */
  extern double median_time;        /* time spent computing medians */
  double        tensor[2][2];       /* inertial tensor */
  double        evec[2];            /* eigenvector of tensor */
  double       *value;              /* values along selected direction to sort */
  double        xcm, ycm;           /* center of mass in each direction */
  double        xx, yy, xy;         /* elements of inertial tensor */
  double        xdif, ydif;         /* deviation from center of mass */
  double        eval, res;          /* eigenvalue and error in eval calculation */
  double        vwgt_sum;           /* sum of all the vertex weights */
  double        time;               /* timing parameters */
  int          *space;              /* space required by median routine */
  int           i;                  /* loop counter */
  double        seconds(void);

  /* Compute center of mass and total mass. */

  time = seconds();
  xcm = ycm = 0.0;
  if (using_vwgts) {
    vwgt_sum = 0.0;
    for (i = 1; i <= nvtxs; i++) {
      vwgt_sum += graph[i]->vwgt;
      xcm += graph[i]->vwgt * x[i];
      ycm += graph[i]->vwgt * y[i];
    }
  }
  else {
    vwgt_sum = nvtxs;
    for (i = 1; i <= nvtxs; i++) {
      xcm += x[i];
      ycm += y[i];
    }
  }

  xcm /= vwgt_sum;
  ycm /= vwgt_sum;

  /* Generate 3 elements of Inertial tensor. */
  xx = yy = xy = 0.0;
  if (using_vwgts) {
    for (i = 1; i <= nvtxs; i++) {
      xdif = x[i] - xcm;
      ydif = y[i] - ycm;
      xx += graph[i]->vwgt * xdif * xdif;
      yy += graph[i]->vwgt * ydif * ydif;
      xy += graph[i]->vwgt * xdif * ydif;
    }
  }
  else {
    for (i = 1; i <= nvtxs; i++) {
      xdif = x[i] - xcm;
      ydif = y[i] - ycm;
      xx += xdif * xdif;
      yy += ydif * ydif;
      xy += xdif * ydif;
    }
  }

  /* Compute eigenvector with maximum eigenvalue. */

  tensor[0][0] = xx;
  tensor[1][1] = yy;
  tensor[1][0] = tensor[0][1] = xy;
  evals2(tensor, &res, &eval);
  eigenvec2(tensor, eval, evec, &res);

  inertial_axis_time += seconds() - time;

  if (DEBUG_INERTIAL > 0) {
    printf("Principle Axis = (%g, %g), Eval=%g, Residual=%e\n", evec[0], evec[1], eval, res);
  }

  /* Allocate space for value array. */

  value = smalloc((nvtxs + 1) * sizeof(double));

  /* Calculate value to sort/split on for each cell. */
  /* This is inner product with eigenvector. */
  for (i = 1; i <= nvtxs; i++) {
    value[i] = (x[i] - xcm) * evec[0] + (y[i] - ycm) * evec[1];
  }

  /* Now find the median value and partition based upon it. */
  space = smalloc(nvtxs * sizeof(int));
  time  = seconds();
  rec_median_1(graph, value, nvtxs, space, cube_or_mesh, nsets, goal, using_vwgts, sets, TRUE);
  median_time += seconds() - time;

  sfree(space);
  sfree(value);
}