/* Reset the basis of a problem, can be usefull in case of degeneracy - JD */
void __declspec(dllexport) WINAPI _reset_basis(lprec *lp)
{
if (lp != NULL) {
freebuferror();
reset_basis(lp);
}
}
int main(void)
{
lprec *lp1,*lp2;
FILE *input_file;
printf("lp_solve 2.0 demo by Jeroen J. Dirks ([email protected])\n\n");
printf("This demo will show most of the features of lp_solve 2.0\n");
press_ret();
printf("\nWe start by creating a new problem with 4 variables and 0 constraints\n");
printf("We use: lp1=make_lp(0,4);\n");
lp1=make_lp(0,4);
press_ret();
printf("We can show the current problem with print_lp(lp1)\n");
print_lp(lp1);
press_ret();
printf("Now we add some constraints\n");
printf("str_add_constraint(lp1, \"3 2 2 1\" ,LE,4)\n");
printf("This is the string version of add_constraint. For the normal version\n");
printf("of add_constraint see the file lpkit.h\n");
str_add_constraint(lp1, "3 2 2 1", LE, 4);
print_lp(lp1);
press_ret();
printf("str_add_constraint(lp1, \"0 4 3 1\" ,GE,3)\n");
str_add_constraint(lp1, "0 4 3 1", GE, 3);
print_lp(lp1);
press_ret();
printf("Set the objective function\n");
printf("str_set_obj_fn(lp1, \"2 3 -2 3\")\n");
str_set_obj_fn(lp1, "2 3 -2 3");
print_lp(lp1);
press_ret();
printf("Now solve the problem with printf(solve(lp1));\n");
printf("%d",solve(lp1));
press_ret();
printf("The value is 0, this means we found an optimal solution\n");
printf("We can display this solution with print_solution(lp1)\n");
print_solution(lp1);
press_ret();
printf("The dual variables of the solution are printed with\n");
printf("print_duals(lp1);\n");
print_duals(lp1);
press_ret();
printf("We can change a single element in the matrix with\n");
printf("set_mat(lp1,2,1,0.5)\n");
set_mat(lp1,2,1,0.5);
print_lp(lp1);
press_ret();
printf("It we want to maximise the objective function use set_maxim(lp1);\n");
set_maxim(lp1);
print_lp(lp1);
press_ret();
printf("after solving this gives us:\n");
solve(lp1);
print_solution(lp1);
print_duals(lp1);
press_ret();
printf("Change the value of a rhs element with set_rh(lp1,1,7.45)\n");
set_rh(lp1,1,7.45);
print_lp(lp1);
solve(lp1);
print_solution(lp1);
press_ret();
printf("We change Var[4] to the integer type with\n");
printf("set_int(lp1, 4, TRUE)\n");
set_int(lp1, 4, TRUE);
print_lp(lp1);
printf("We set branch & bound debugging on with lp1->debug=TRUE\n");
lp1->debug=TRUE;
printf("and solve...\n");
press_ret();
solve(lp1);
print_solution(lp1);
press_ret();
printf("We can set bounds on the variables with\n");
printf("set_lowbo(lp1,2,2); & set_upbo(lp1,4,5.3)\n");
set_lowbo(lp1,2,2);
set_upbo(lp1,4,5.3);
print_lp(lp1);
press_ret();
solve(lp1);
print_solution(lp1);
press_ret();
printf("Now remove a constraint with del_constraint(lp1, 1)\n");
del_constraint(lp1,1);
print_lp(lp1);
printf("Add an equality constraint\n");
str_add_constraint(lp1, "1 2 1 4", EQ, 8);
print_lp(lp1);
press_ret();
printf("A column can be added with:\n");
printf("str_add_column(lp1,\"3 2 2\");\n");
str_add_column(lp1,"3 2 2");
print_lp(lp1);
press_ret();
printf("A column can be removed with:\n");
printf("del_column(lp1,3);\n");
del_column(lp1,3);
print_lp(lp1);
press_ret();
printf("We can use automatic scaling with:\n");
printf("auto_scale(lp1);\n");
auto_scale(lp1);
print_lp(lp1);
press_ret();
printf("The function mat_elm(lprec *lp, int row, int column) returns a single\n");
printf("matrix element\n");
printf("%s mat_elm(lp1,2,3), mat_elm(lp1,1,1); gives\n","printf(\"%f %f\\n\",");
printf("%f %f\n",mat_elm(lp1,2,3), mat_elm(lp1,1,1));
printf("Notice that mat_elm returns the value of the original unscaled problem\n");
press_ret();
printf("It there are any integer type variables, then only the rows are scaled\n");
printf("set_int(lp1,3,FALSE);\n");
printf("auto_scale(lp1);\n");
set_int(lp1,3,FALSE);
auto_scale(lp1);
print_lp(lp1);
press_ret();
solve(lp1);
printf("print_solution gives the solution to the original problem\n");
print_solution(lp1);
press_ret();
printf("Scaling is turned off with unscale(lp1);\n");
unscale(lp1);
print_lp(lp1);
press_ret();
printf("Now turn B&B debugging of and simplex tracing on with\n");
printf("lp1->debug=FALSE, lp1->trace=TRUE and solve(lp1)\n");
lp1->debug=FALSE;
lp1->trace=TRUE;
press_ret();
solve(lp1);
printf("Where possible, lp_solve will start at the last found basis\n");
printf("We can reset the problem to the initial basis with\n");
printf("reset_basis(lp1). Now solve it again...\n");
press_ret();
reset_basis(lp1);
solve(lp1);
press_ret();
printf("It is possible to give variables and constraints names\n");
printf("set_row_name(lp1,1,\"speed\"); & set_col_name(lp1,2,\"money\")\n");
set_row_name(lp1,1,"speed");
set_col_name(lp1,2,"money");
print_lp(lp1);
printf("As you can see, all column and rows are assigned default names\n");
printf("If a column or constraint is deleted, the names shift place also:\n");
press_ret();
printf("del_column(lp1,1);\n");
del_column(lp1,1);
print_lp(lp1);
press_ret();
printf("A lp structure can be created and read from a .lp file\n");
printf("input_file=fopen(\"lp_examples/demo_lag.lp\",\"r\");\n");
printf("lp2 = read_lp_file(input_file, TRUE);\n");
printf("The verbose option is used\n");
input_file = fopen("lp_examples/demo_lag.lp", "r");
if (input_file == NULL)
{
printf("Can't find demo_lag.lp, stopping\n");
exit(EXIT_FAILURE);
}
lp2 = read_lp_file(input_file, TRUE, "test");
press_ret();
printf("lp2 is now:\n");
print_lp(lp2);
press_ret();
printf("solution:\n");
lp2->debug=TRUE;
solve(lp2);
lp2->debug=FALSE;
print_solution(lp2);
press_ret();
printf("You can see that branch & bound was used in this problem\n");
printf("Now remove the last constraint and use lagrangian relaxation\n");
printf("del_constraint(lp2,6);\n");
printf("str_add_lag_con(lp2, \"1 1 1 0 0 0\", LE, 2);\n");
del_constraint(lp2,6);
str_add_lag_con(lp2, "1 1 1 0 0 0", LE, 2);
print_lp(lp2);
printf("Lagrangian relaxation is used in some heuristics. It is now possible\n");
printf("to get a feasible integer soltution without usage of branch & bound.\n");
printf("Use lag_solve(lp2, 0, 40, TRUE); 0 is the initial bound, 30 the maximum\n");
printf("number of iterations, the last variable turns the verbose mode on.\n");
press_ret();
printf("%d\n",lag_solve(lp2, 0, 30, TRUE));
printf("The returncode of lag_solve is 6 or FEAS_FOUND. this means that a feasible\n");
printf("solution has been found. For a list of other possible return values\n");
printf("see \"lpkit.h\". Print this solution with print_solution\n");
print_solution(lp2);
press_ret();
return(0);
}
