add_constraint, add_constraintex, str_add_constraint

Add a constraint to the lp.

unsigned char add_constraint(lprec *lp, REAL *row, int constr_type, REAL rh);

unsigned char add_constraintex(lprec *lp, int count, REAL *row, int *colno, int constr_type, REAL rh);

unsigned char str_add_constraint(lprec *lp, char *row_string, int constr_type, REAL rh);

Return Value

add_constraint, add_constraintex and str_add_constraint return TRUE (1) if the operation was successful. A return value of FALSE (0) indicates an error.

Parameters

Pointer to previously created lp model. See return value of make_lp, read_lp, read_LP, read_mps, read_freemps, read_MPS, read_freeMPS, read_XLI

count

Number of elements in row and colno.

row

An array with 1+column (count for add_constraintex if colno is different from NULL) elements that contains the values of the row.

colno

An array with count elements that contains the column numbers of the row. However this variable can also be NULL. In that case element i in the variable row is column i and values start at element 1.

row_string

A string with column elements that contains the values of the row. Each element must be separated by space(s).

constr_type

The type of the constraint. Can by any of the following values:

LE (1)	Less than or equal (<=)
EQ (3)	Equal (=)
GE (2)	Greater than or equal (>=)

The value of the right hand side (RHS).

Remarks

The add_constraint, add_constraintex, str_add_constraint functions add a row to the model (at the end) and sets all values of the row at once.
Note that for add_constraint (and add_constraintex when colno is NULL) element 0 of the array is not considered (i.e. ignored). Column 1 is element 1, column 2 is element 2, ...
add_constraintex has the possibility to specify only the non-zero elements. In that case colno specifies the column numbers of the non-zero elements. This will speed up building the model considerably if there are a lot of zero values. In most cases the matrix is sparse and has many zero value. Thus it is almost always better to use add_constraintex instead of add_constraint. add_constraintex is always at least as performant as add_constraint. Note that these routines will perform much better when set_add_rowmode is called before adding constraints.
Note that it is advised to set the objective function (via set_obj_fn, set_obj_fnex, str_set_obj_fn, set_obj) before adding rows. This especially for larger models. This will be much more performant than adding the objective function afterwards.

Example

#include <stdio.h>
#include <stdlib.h>
#include "lp_lib.h"

int main(void)
{
  lprec *lp;
  REAL row[1+2]; /* must be 1 more then number of columns ! */

  /* Create a new LP model */
  lp = make_lp(0, 2);
  if(lp == NULL) {
    fprintf(stderr, "Unable to create new LP model\n");
    return(1);
  }

  set_add_rowmode(lp, TRUE);
  row[1] = 1.0;
  row[2] = 2.0;
  add_constraint(lp, row, GE, 3.0); /* constructs the row: +v_1 +2 v_2 >= 3 */
  set_add_rowmode(lp, FALSE);

  delete_lp(lp);
  return(0);
}

lp_solve API reference