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/* spv.c (operations on sparse vectors) */
/***********************************************************************
* This code is part of GLPK (GNU Linear Programming Kit).
*
* Copyright (C) 2007-2017 Andrew Makhorin, Department for Applied
* Informatics, Moscow Aviation Institute, Moscow, Russia. All rights
* reserved. E-mail: <mao@gnu.org>.
*
* GLPK is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* GLPK is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
* License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GLPK. If not, see <http://www.gnu.org/licenses/>.
***********************************************************************/
#include "env.h"
#include "spv.h"
/***********************************************************************
* NAME
*
* spv_create_vec - create sparse vector
*
* SYNOPSIS
*
* #include "glpios.h"
* SPV *spv_create_vec(int n);
*
* DESCRIPTION
*
* The routine spv_create_vec creates a sparse vector of dimension n,
* which initially is a null vector.
*
* RETURNS
*
* The routine returns a pointer to the vector created. */
SPV *spv_create_vec(int n)
{ SPV *v;
xassert(n >= 0);
v = xmalloc(sizeof(SPV));
v->n = n;
v->nnz = 0;
v->pos = xcalloc(1+n, sizeof(int));
memset(&v->pos[1], 0, n * sizeof(int));
v->ind = xcalloc(1+n, sizeof(int));
v->val = xcalloc(1+n, sizeof(double));
return v;
}
/***********************************************************************
* NAME
*
* spv_check_vec - check that sparse vector has correct representation
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_check_vec(SPV *v);
*
* DESCRIPTION
*
* The routine spv_check_vec checks that a sparse vector specified by
* the parameter v has correct representation.
*
* NOTE
*
* Complexity of this operation is O(n). */
void spv_check_vec(SPV *v)
{ int j, k, nnz;
xassert(v->n >= 0);
nnz = 0;
for (j = v->n; j >= 1; j--)
{ k = v->pos[j];
xassert(0 <= k && k <= v->nnz);
if (k != 0)
{ xassert(v->ind[k] == j);
nnz++;
}
}
xassert(v->nnz == nnz);
return;
}
/***********************************************************************
* NAME
*
* spv_get_vj - retrieve component of sparse vector
*
* SYNOPSIS
*
* #include "glpios.h"
* double spv_get_vj(SPV *v, int j);
*
* RETURNS
*
* The routine spv_get_vj returns j-th component of a sparse vector
* specified by the parameter v. */
double spv_get_vj(SPV *v, int j)
{ int k;
xassert(1 <= j && j <= v->n);
k = v->pos[j];
xassert(0 <= k && k <= v->nnz);
return (k == 0 ? 0.0 : v->val[k]);
}
/***********************************************************************
* NAME
*
* spv_set_vj - set/change component of sparse vector
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_set_vj(SPV *v, int j, double val);
*
* DESCRIPTION
*
* The routine spv_set_vj assigns val to j-th component of a sparse
* vector specified by the parameter v. */
void spv_set_vj(SPV *v, int j, double val)
{ int k;
xassert(1 <= j && j <= v->n);
k = v->pos[j];
if (val == 0.0)
{ if (k != 0)
{ /* remove j-th component */
v->pos[j] = 0;
if (k < v->nnz)
{ v->pos[v->ind[v->nnz]] = k;
v->ind[k] = v->ind[v->nnz];
v->val[k] = v->val[v->nnz];
}
v->nnz--;
}
}
else
{ if (k == 0)
{ /* create j-th component */
k = ++(v->nnz);
v->pos[j] = k;
v->ind[k] = j;
}
v->val[k] = val;
}
return;
}
/***********************************************************************
* NAME
*
* spv_clear_vec - set all components of sparse vector to zero
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_clear_vec(SPV *v);
*
* DESCRIPTION
*
* The routine spv_clear_vec sets all components of a sparse vector
* specified by the parameter v to zero. */
void spv_clear_vec(SPV *v)
{ int k;
for (k = 1; k <= v->nnz; k++)
v->pos[v->ind[k]] = 0;
v->nnz = 0;
return;
}
/***********************************************************************
* NAME
*
* spv_clean_vec - remove zero or small components from sparse vector
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_clean_vec(SPV *v, double eps);
*
* DESCRIPTION
*
* The routine spv_clean_vec removes zero components and components
* whose magnitude is less than eps from a sparse vector specified by
* the parameter v. If eps is 0.0, only zero components are removed. */
void spv_clean_vec(SPV *v, double eps)
{ int k, nnz;
nnz = 0;
for (k = 1; k <= v->nnz; k++)
{ if (fabs(v->val[k]) == 0.0 || fabs(v->val[k]) < eps)
{ /* remove component */
v->pos[v->ind[k]] = 0;
}
else
{ /* keep component */
nnz++;
v->pos[v->ind[k]] = nnz;
v->ind[nnz] = v->ind[k];
v->val[nnz] = v->val[k];
}
}
v->nnz = nnz;
return;
}
/***********************************************************************
* NAME
*
* spv_copy_vec - copy sparse vector (x := y)
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_copy_vec(SPV *x, SPV *y);
*
* DESCRIPTION
*
* The routine spv_copy_vec copies a sparse vector specified by the
* parameter y to a sparse vector specified by the parameter x. */
void spv_copy_vec(SPV *x, SPV *y)
{ int j;
xassert(x != y);
xassert(x->n == y->n);
spv_clear_vec(x);
x->nnz = y->nnz;
memcpy(&x->ind[1], &y->ind[1], x->nnz * sizeof(int));
memcpy(&x->val[1], &y->val[1], x->nnz * sizeof(double));
for (j = 1; j <= x->nnz; j++)
x->pos[x->ind[j]] = j;
return;
}
/***********************************************************************
* NAME
*
* spv_linear_comb - compute linear combination (x := x + a * y)
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_linear_comb(SPV *x, double a, SPV *y);
*
* DESCRIPTION
*
* The routine spv_linear_comb computes the linear combination
*
* x := x + a * y,
*
* where x and y are sparse vectors, a is a scalar. */
void spv_linear_comb(SPV *x, double a, SPV *y)
{ int j, k;
double xj, yj;
xassert(x != y);
xassert(x->n == y->n);
for (k = 1; k <= y->nnz; k++)
{ j = y->ind[k];
xj = spv_get_vj(x, j);
yj = y->val[k];
spv_set_vj(x, j, xj + a * yj);
}
return;
}
/***********************************************************************
* NAME
*
* spv_delete_vec - delete sparse vector
*
* SYNOPSIS
*
* #include "glpios.h"
* void spv_delete_vec(SPV *v);
*
* DESCRIPTION
*
* The routine spv_delete_vec deletes a sparse vector specified by the
* parameter v freeing all the memory allocated to this object. */
void spv_delete_vec(SPV *v)
{ /* delete sparse vector */
xfree(v->pos);
xfree(v->ind);
xfree(v->val);
xfree(v);
return;
}
/* eof */
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