source: inundation/pyvolution/quantity_ext.c @ 2018

// Python - C extension for quantity module.
//
// To compile (Python2.3):
//  gcc -c util_ext.c -I/usr/include/python2.3 -o util_ext.o -Wall -O
//  gcc -shared util_ext.o  -o util_ext.so
//
// See the module quantity.py
//
//
// Ole Nielsen, GA 2004

#include "Python.h"
#include "Numeric/arrayobject.h"
#include "math.h"

//Shared code snippets
#include "util_ext.h"
//#include "quantity_ext.h" //Obsolete



int _compute_gradients(int N,
                        double* centroids,
                        double* centroid_values,
                        long* number_of_boundaries,
                        long* surrogate_neighbours,
                        double* a,
                        double* b) {

  int i, k, k0, k1, k2, index3;
  double x0, x1, x2, y0, y1, y2, q0, q1, q2; //, det;


  for (k=0; k<N; k++) {
    index3 = 3*k;

    if (number_of_boundaries[k] < 2) {
      //Two or three true neighbours

      //Get indices of neighbours (or self when used as surrogate)
      //k0, k1, k2 = surrogate_neighbours[k,:]

      k0 = surrogate_neighbours[index3 + 0];
      k1 = surrogate_neighbours[index3 + 1];
      k2 = surrogate_neighbours[index3 + 2];


      if (k0 == k1 || k1 == k2) return -1;

      //Get data
      q0 = centroid_values[k0];
      q1 = centroid_values[k1];
      q2 = centroid_values[k2];

      x0 = centroids[k0*2]; y0 = centroids[k0*2+1];
      x1 = centroids[k1*2]; y1 = centroids[k1*2+1];
      x2 = centroids[k2*2]; y2 = centroids[k2*2+1];

      //Gradient
      _gradient(x0, y0, x1, y1, x2, y2, q0, q1, q2, &a[k], &b[k]);

    } else if (number_of_boundaries[k] == 2) {
      //One true neighbour

      //#Get index of the one neighbour
      i=0; k0 = k;
      while (i<3 && k0==k) {
        k0 = surrogate_neighbours[index3 + i];
        i++;
      }
      if (k0 == k) return -1;

      k1 = k; //self

      //Get data
      q0 = centroid_values[k0];
      q1 = centroid_values[k1];

      x0 = centroids[k0*2]; y0 = centroids[k0*2+1];
      x1 = centroids[k1*2]; y1 = centroids[k1*2+1];

      //Two point gradient
      _gradient2(x0, y0, x1, y1, q0, q1, &a[k], &b[k]);      
      
      
      //Old (wrong code)
      //det = x0*y1 - x1*y0;
      //if (det != 0.0) {
      //        a[k] = (y1*q0 - y0*q1)/det;
      //        b[k] = (x0*q1 - x1*q0)/det;
      //}
    }
    //    else:
    //        #No true neighbours -
    //        #Fall back to first order scheme
    //        pass
  }
  return 0;
}


int _extrapolate(int N,
                 double* centroids,
                 double* centroid_values,
                 double* vertex_coordinates,
                 double* vertex_values,
                 double* a,
                 double* b) {

  int k, k2, k3, k6;
  double x, y, x0, y0, x1, y1, x2, y2;

  for (k=0; k<N; k++) {
    k6 = 6*k;
    k3 = 3*k;
    k2 = 2*k;

    //Centroid coordinates
    x = centroids[k2]; y = centroids[k2+1];

    //vertex coordinates
    //x0, y0, x1, y1, x2, y2 = X[k,:]
    x0 = vertex_coordinates[k6 + 0];
    y0 = vertex_coordinates[k6 + 1];
    x1 = vertex_coordinates[k6 + 2];
    y1 = vertex_coordinates[k6 + 3];
    x2 = vertex_coordinates[k6 + 4];
    y2 = vertex_coordinates[k6 + 5];

    //Extrapolate
    vertex_values[k3+0] = centroid_values[k] + a[k]*(x0-x) + b[k]*(y0-y);
    vertex_values[k3+1] = centroid_values[k] + a[k]*(x1-x) + b[k]*(y1-y);
    vertex_values[k3+2] = centroid_values[k] + a[k]*(x2-x) + b[k]*(y2-y);

  }
  return 0;
}




int _interpolate(int N,
                 double* vertex_values,
                 double* edge_values) {

  int k, k3;
  double q0, q1, q2;


  for (k=0; k<N; k++) {
    k3 = 3*k;

    q0 = vertex_values[k3 + 0];
    q1 = vertex_values[k3 + 1];
    q2 = vertex_values[k3 + 2];

    //printf("%f, %f, %f\n", q0, q1, q2);
    edge_values[k3 + 0] = 0.5*(q1+q2);
    edge_values[k3 + 1] = 0.5*(q0+q2);
    edge_values[k3 + 2] = 0.5*(q0+q1);
  }
  return 0;
}

int _update(int N,
            double timestep,
            double* centroid_values,
            double* explicit_update,
            double* semi_implicit_update) {
  //Update centroid values based on values stored in
  //explicit_update and semi_implicit_update as well as given timestep


  int k;
  double denominator, x;


  //Divide semi_implicit update by conserved quantity
  for (k=0; k<N; k++) {
    x = centroid_values[k];
    if (x == 0.0) {
      semi_implicit_update[k] = 0.0;
    } else {
      semi_implicit_update[k] /= x;
    }
  }


  //Explicit updates
  for (k=0; k<N; k++) {
    centroid_values[k] += timestep*explicit_update[k];
  }

  //Semi implicit updates
  for (k=0; k<N; k++) {
    denominator = 1.0 - timestep*semi_implicit_update[k];
    if (denominator == 0.0) {
      return -1;
    } else {
      //Update conserved_quantities from semi implicit updates
      centroid_values[k] /= denominator;
    }
  }
  //MH080605 set semi_impliit_update[k] to 0.0 here, rather than in update_conserved_quantities.py
  for (k=0;k<N;k++)
    semi_implicit_update[k]=0.0;
  return 0;
}


/////////////////////////////////////////////////
// Gateways to Python
PyObject *update(PyObject *self, PyObject *args) {

  PyObject *quantity;
  PyArrayObject *centroid_values, *explicit_update, *semi_implicit_update;

  double timestep;
  int N, err;


  // Convert Python arguments to C
  if (!PyArg_ParseTuple(args, "Od", &quantity, &timestep))
    return NULL;

  centroid_values = get_consecutive_array(quantity, "centroid_values");
  explicit_update = get_consecutive_array(quantity, "explicit_update");
  semi_implicit_update = get_consecutive_array(quantity, "semi_implicit_update");

  N = centroid_values -> dimensions[0];

  err = _update(N, timestep,
                (double*) centroid_values -> data,
                (double*) explicit_update -> data,
                (double*) semi_implicit_update -> data);


  if (err != 0) {
    PyErr_SetString(PyExc_RuntimeError,
                    "Zero division in semi implicit update - call Stephen :)");
    return NULL;
  }

  //Release and return
  Py_DECREF(centroid_values);
  Py_DECREF(explicit_update);
  Py_DECREF(semi_implicit_update);

  return Py_BuildValue("");
}


PyObject *interpolate_from_vertices_to_edges(PyObject *self, PyObject *args) {

  PyObject *quantity;
  PyArrayObject *vertex_values, *edge_values;

  int N, err;

  // Convert Python arguments to C
  if (!PyArg_ParseTuple(args, "O", &quantity))
    return NULL;

  vertex_values = get_consecutive_array(quantity, "vertex_values");
  edge_values = get_consecutive_array(quantity, "edge_values");

  N = vertex_values -> dimensions[0];

  err = _interpolate(N,
                     (double*) vertex_values -> data,
                     (double*) edge_values -> data);

  if (err != 0) {
    PyErr_SetString(PyExc_RuntimeError, "Interpolate could not be computed");
    return NULL;
  }

  //Release and return
  Py_DECREF(vertex_values);
  Py_DECREF(edge_values);

  return Py_BuildValue("");
}


PyObject *compute_gradients(PyObject *self, PyObject *args) {

  PyObject *quantity, *domain, *R;
  PyArrayObject
    *centroids,            //Coordinates at centroids
    *centroid_values,      //Values at centroids
    *number_of_boundaries, //Number of boundaries for each triangle
    *surrogate_neighbours, //True neighbours or - if one missing - self
    *a, *b;                //Return values

  int dimensions[1], N, err;

  // Convert Python arguments to C
  if (!PyArg_ParseTuple(args, "O", &quantity))
    return NULL;

  domain = PyObject_GetAttrString(quantity, "domain");
  if (!domain)
    return NULL;

  //Get pertinent variables

  centroids = get_consecutive_array(domain, "centroid_coordinates");
  centroid_values = get_consecutive_array(quantity, "centroid_values");
  surrogate_neighbours = get_consecutive_array(domain, "surrogate_neighbours");
  number_of_boundaries = get_consecutive_array(domain, "number_of_boundaries");

  N = centroid_values -> dimensions[0];

  //Release
  Py_DECREF(domain);

  //Allocate space for return vectors a and b (don't DECREF)
  dimensions[0] = N;
  a = (PyArrayObject *) PyArray_FromDims(1, dimensions, PyArray_DOUBLE);
  b = (PyArrayObject *) PyArray_FromDims(1, dimensions, PyArray_DOUBLE);



  err = _compute_gradients(N,
                           (double*) centroids -> data,
                           (double*) centroid_values -> data,
                           (long*) number_of_boundaries -> data,
                           (long*) surrogate_neighbours -> data,
                           (double*) a -> data,
                           (double*) b -> data);

  if (err != 0) {
    PyErr_SetString(PyExc_RuntimeError, "Gradient could not be computed");
    return NULL;
  }

  //Release
  Py_DECREF(centroids);
  Py_DECREF(centroid_values);
  Py_DECREF(number_of_boundaries);
  Py_DECREF(surrogate_neighbours);

  //Build result, release and return
  R = Py_BuildValue("OO", PyArray_Return(a), PyArray_Return(b));
  Py_DECREF(a);
  Py_DECREF(b);
  return R;
}



PyObject *extrapolate_second_order(PyObject *self, PyObject *args) {

  PyObject *quantity, *domain;
  PyArrayObject
    *centroids,            //Coordinates at centroids
    *centroid_values,      //Values at centroids
    *vertex_coordinates,   //Coordinates at vertices
    *vertex_values,        //Values at vertices
    *number_of_boundaries, //Number of boundaries for each triangle
    *surrogate_neighbours, //True neighbours or - if one missing - self
    *a, *b;                //Gradients

  //int N, err;
  int dimensions[1], N, err;
  //double *a, *b;  //Gradients

  // Convert Python arguments to C
  if (!PyArg_ParseTuple(args, "O", &quantity))
    return NULL;

  domain = PyObject_GetAttrString(quantity, "domain");
  if (!domain)
    return NULL;

  //Get pertinent variables
  centroids = get_consecutive_array(domain, "centroid_coordinates");
  centroid_values = get_consecutive_array(quantity, "centroid_values");
  surrogate_neighbours = get_consecutive_array(domain, "surrogate_neighbours");
  number_of_boundaries = get_consecutive_array(domain, "number_of_boundaries");
  vertex_coordinates = get_consecutive_array(domain, "vertex_coordinates");
  vertex_values = get_consecutive_array(quantity, "vertex_values");

  N = centroid_values -> dimensions[0];

  //Release
  Py_DECREF(domain);

  //Allocate space for return vectors a and b (don't DECREF)
  dimensions[0] = N;
  a = (PyArrayObject *) PyArray_FromDims(1, dimensions, PyArray_DOUBLE);
  b = (PyArrayObject *) PyArray_FromDims(1, dimensions, PyArray_DOUBLE);

  //FIXME: Odd that I couldn't use normal arrays
  //Allocate space for return vectors a and b (don't DECREF)
  //a = (double*) malloc(N * sizeof(double));
  //if (!a) return NULL;
  //b = (double*) malloc(N * sizeof(double));
  //if (!b) return NULL;


  err = _compute_gradients(N,
                           (double*) centroids -> data,
                           (double*) centroid_values -> data,
                           (long*) number_of_boundaries -> data,
                           (long*) surrogate_neighbours -> data,
                           (double*) a -> data,
                           (double*) b -> data);

  if (err != 0) {
    PyErr_SetString(PyExc_RuntimeError, "Gradient could not be computed");
    return NULL;
  }

  err = _extrapolate(N,
                     (double*) centroids -> data,
                     (double*) centroid_values -> data,
                     (double*) vertex_coordinates -> data,
                     (double*) vertex_values -> data,
                     (double*) a -> data,
                     (double*) b -> data);


  if (err != 0) {
    PyErr_SetString(PyExc_RuntimeError,
                    "Internal function _extrapolate failed");
    return NULL;
  }



  //Release
  Py_DECREF(centroids);
  Py_DECREF(centroid_values);
  Py_DECREF(number_of_boundaries);
  Py_DECREF(surrogate_neighbours);
  Py_DECREF(vertex_coordinates);
  Py_DECREF(vertex_values);
  Py_DECREF(a);
  Py_DECREF(b);

  return Py_BuildValue("");
}



PyObject *limit(PyObject *self, PyObject *args) {

  PyObject *quantity, *domain, *Tmp;
  PyArrayObject
    *qv, //Conserved quantities at vertices
    *qc, //Conserved quantities at centroids
    *neighbours;

  int k, i, n, N, k3;
  double beta_w; //Safety factor
  double *qmin, *qmax, qn;

  // Convert Python arguments to C
  if (!PyArg_ParseTuple(args, "O", &quantity))
    return NULL;

  domain = PyObject_GetAttrString(quantity, "domain");
  if (!domain)
    return NULL;

  //neighbours = (PyArrayObject*) PyObject_GetAttrString(domain, "neighbours");
  neighbours = get_consecutive_array(domain, "neighbours");

  //Get safety factor beta_w
  Tmp = PyObject_GetAttrString(domain, "beta_w");
  if (!Tmp)
    return NULL;

  beta_w = PyFloat_AsDouble(Tmp);

  Py_DECREF(Tmp);
  Py_DECREF(domain);


  qc = get_consecutive_array(quantity, "centroid_values");
  qv = get_consecutive_array(quantity, "vertex_values");


  N = qc -> dimensions[0];

  //Find min and max of this and neighbour's centroid values
  qmin = malloc(N * sizeof(double));
  qmax = malloc(N * sizeof(double));
  for (k=0; k<N; k++) {
    k3=k*3;

    qmin[k] = ((double*) qc -> data)[k];
    qmax[k] = qmin[k];

    for (i=0; i<3; i++) {
      n = ((long*) neighbours -> data)[k3+i];
      if (n >= 0) {
        qn = ((double*) qc -> data)[n]; //Neighbour's centroid value

        qmin[k] = min(qmin[k], qn);
        qmax[k] = max(qmax[k], qn);
      }
    }
  }

  // Call underlying routine
  _limit(N, beta_w, (double*) qc -> data, (double*) qv -> data, qmin, qmax);

  free(qmin);
  free(qmax);
  return Py_BuildValue("");
}



// Method table for python module
static struct PyMethodDef MethodTable[] = {
  {"limit", limit, METH_VARARGS, "Print out"},
  {"update", update, METH_VARARGS, "Print out"},
  {"compute_gradients", compute_gradients, METH_VARARGS, "Print out"},
  {"extrapolate_second_order", extrapolate_second_order,
   METH_VARARGS, "Print out"},
  {"interpolate_from_vertices_to_edges",
   interpolate_from_vertices_to_edges,
   METH_VARARGS, "Print out"},
  {NULL, NULL, 0, NULL}   // sentinel
};

// Module initialisation
void initquantity_ext(void){
  Py_InitModule("quantity_ext", MethodTable);

  import_array();     //Necessary for handling of NumPY structures
}