Re: [Fwd: GLPK for Java]

On 09/16/2017 03:01 PM, Andrew Makhorin wrote:
> -------- Forwarded Message --------
> From: [email protected]
> To: [email protected] <[email protected]>
> Subject: GLPK for Java
> Date: Sat, 16 Sep 2017 14:03:45 +0200
> 
> Dear All --
> 

In many aspects your code does not correlate to the problem you want to
solve.
Read doc/glpk.pdf carefully and try to understand the example code.
Check every value you pass to glp_set_mat_row in the line of code
causing the error. What is ind[] used for? What does len = 2 mean?

>  
> 
> We have already run several GMPL examples with WinGLPK but need to solve
> linear programs in our Java application. I imported glpk-4.63\examples
> \java into an Eclipse Project so I am able to run the examples now. In
> particular we need to do call GLPK as shown in Lp.java which I wanted to
> modify such that it first solves another simple example whose GMPL code
> is as follows:
> 
> 
>  
> 
> 
>             minimize z = -3 * x1 - x2
> 
> 
>  
> 
> 
>             subject to
> 
> 
>                                          2 * x2   <=  6
> 
> 
>                             2 * x1 + 3 * x2  <= 13
> 
> 
>                   2 <=       x1                <=  5
> 
> 
>             where,
> 
> 
>                 0.0 <= x1
> 
> 
>                 0.0 <= x2
> 
> 
>  
> 
> Unfortunately my modification of Lp.java results in the error
> 
>  
> 
> glp_set_mat_row: i = 1; ind[2] = 0; column index out of range
> 
> 
> Error detected in file ..\src\api\prob1.c at line 773
> 
> 
> org.gnu.glpk.GlpkException: function glp_set_mat_row failed
> 
> 
>          at org.gnu.glpk.GLPKJNI.glp_set_mat_row(Native Method)
> 
> 
>          at org.gnu.glpk.GLPK.glp_set_mat_row(GLPK.java:382)
> 
> 
>  
> 
> but although I have found the Javadoc I seems difficult to me to explain
> the reason for my error.
> 
>  
> 
> My questions are
> 
>  
> 
>      1. Can anybody explain this error?
>      2. Is is possible to create the GPLK for Java problem instances by
>         loading GMPL source code from a file?
>      3. Can we write a problem correctly created with GPLK for Java to a
>         GMPL source code file on disk?
>  
> 
> The answer to Q3 is the line
> 
>  
> 
> 
> GLPK.glp_write_lp(lp, null, "mincost.lp");
> 
> 
>  
> 
> which I found in the example MinimumCostFlow.java so 
> 
>  
> 
> glp_read_lp
> public static int glp_read_lp(glp_prob P,
>                               glp_cpxcp parm,
>                               String fname)
>  
> 
> should be the answer to Q2. If the latter will help me load the above
> GMPL Problem into GLPK and GPLK for Java could generate a Java source
> file creating an instance of the Problem that has been loaded into an
> GLPK object then my current Problem would be solved.
> 
> 
> 
>  
> 
>       * Is somebody able to devise a general method for generating the
>         Java source creating a GLPK instance which represents a problem
>         described by GMPL code above?
> 
>  
> 
>  
> 
> This is my current Code:
> 
>  
> 
> import org.gnu.glpk.GLPK;
> 
> import org.gnu.glpk.GLPKConstants;
> 
> import org.gnu.glpk.GlpkException;
> 
> import org.gnu.glpk.SWIGTYPE_p_double;
> 
> import org.gnu.glpk.SWIGTYPE_p_int;
> 
> import org.gnu.glpk.glp_prob;
> 
> import org.gnu.glpk.glp_smcp;
> 
>  
> 
> public class Produktionsplanung {
> 
>     //     Minimize z = -3 * x1 - x2
> 
>     //
> 
>     //     subject to
> 
>     //              2 * x2  <=  6
> 
>     //     2 * x1 + 3 * x2  <= 13
> 
>     //         x1           <=  5
> 
>     //     where,
> 
>     //     0.0 <= x1
> 
>     //     0.0 <= x2
> 
>  
> 
>     public static void main(String[] arg) {
> 
>         glp_prob lp;
> 
>         glp_smcp parm;
> 
>         SWIGTYPE_p_int ind;
> 
>         SWIGTYPE_p_double val;
> 
>         int ret;
> 
>  
> 
>         try {
> 
>             // Create problem
> 
>             lp = GLPK.glp_create_prob();
> 
>             System.out.println("Problem created");
> 
>             GLPK.glp_set_prob_name(lp, "myProblem");
> 
>  
> 
>             // Define one column per variable (2)
> 
>             GLPK.glp_add_cols(lp, 2);
> 
>             GLPK.glp_set_col_name(lp, 1, "x1");
> 
>             GLPK.glp_set_col_kind(lp, 1, GLPKConstants.GLP_CV);
> 
>             GLPK.glp_set_col_bnds(lp, 1, GLPKConstants.GLP_DB, 0, 100);
> 
>             GLPK.glp_set_col_name(lp, 2, "x2");
> 
>             GLPK.glp_set_col_kind(lp, 2, GLPKConstants.GLP_CV);
> 
>             GLPK.glp_set_col_bnds(lp, 2, GLPKConstants.GLP_DB, 0, 100);
> 
>  
> 
>             // Create constraints
> 
>  
> 
>             // Allocate memory
> 
>             ind = GLPK.new_intArray(3);
> 
>             val = GLPK.new_doubleArray(2);
> 
>  
> 
>             // Create one row per constraint (3)
> 
>             GLPK.glp_add_rows(lp, 3);
> 
>  
> 
>             // Set row details
> 
>             // subject to 2 * x2 <=  6
> 
>             GLPK.glp_set_row_name(lp, 1, "c1");
> 
>             GLPK.glp_set_row_bnds(lp, 1, GLPKConstants.GLP_DB, 0, 6);
> 
>             GLPK.intArray_setitem(ind, 1, 2);
> 
>             GLPK.doubleArray_setitem(val, 1, 2);
> 
>             GLPK.glp_set_mat_row(lp, 1, 2, ind, val);
> 
>  
> 
>             // subject to  2 * x1 + 3 * x2 <= 13
> 
>             GLPK.glp_set_row_name(lp, 2, "c2");
> 
>             GLPK.glp_set_row_bnds(lp, 2, GLPKConstants.GLP_UP, 0, 13);
> 
>             GLPK.intArray_setitem(ind, 1, 1);
> 
>             GLPK.intArray_setitem(ind, 2, 2);
> 
>             GLPK.doubleArray_setitem(val, 1, 2);
> 
>             GLPK.doubleArray_setitem(val, 2, 3);
> 
>             GLPK.glp_set_mat_row(lp, 2, 2, ind, val);
> 
>  
> 
>             // subject to  x1          <=  5
> 
>             GLPK.glp_set_row_name(lp, 3, "c3");
> 
>             GLPK.glp_set_row_bnds(lp, 3, GLPKConstants.GLP_UP, 0, 5);
> 
>             GLPK.intArray_setitem(ind, 1, 1);
> 
>             GLPK.doubleArray_setitem(val, 1, 1);
> 
>             GLPK.glp_set_mat_row(lp, 2, 2, ind, val);
> 
>  
> 
>             // Free memory
> 
>             GLPK.delete_intArray(ind);
> 
>             GLPK.delete_doubleArray(val);
> 
>  
> 
>             // Define objective
> 
>             GLPK.glp_set_obj_name(lp, "z");
> 
>             GLPK.glp_set_obj_dir(lp, GLPKConstants.GLP_MIN);
> 
>             GLPK.glp_set_obj_coef(lp, 0, 1.);
> 
>             GLPK.glp_set_obj_coef(lp, 1, -.5);
> 
>             GLPK.glp_set_obj_coef(lp, 2, .5);
> 
>             GLPK.glp_set_obj_coef(lp, 3, -1);
> 
>  
> 
>             // Write model to file
> 
>             // GLPK.glp_write_lp(lp, null, "lp.lp");
> 
>  
> 
>             // Solve model
> 
>             parm = new glp_smcp();
> 
>             GLPK.glp_init_smcp(parm);
> 
>             ret = GLPK.glp_simplex(lp, parm);
> 
>  
> 
>             // Retrieve solution
> 
>             if (ret == 0) {
> 
>                 write_lp_solution(lp);
> 
>             } else {
> 
>                 System.out.println("The problem could not be solved");
> 
>             }
> 
>  
> 
>             // Free memory
> 
>             GLPK.glp_delete_prob(lp);
> 
>         } catch (GlpkException ex) {
> 
>             ex.printStackTrace();
> 
>          ret = 1;
> 
>         }
> 
>      System.exit(ret);
> 
>     }
> 
>  
> 
>     /**
> 
>      * write simplex solution
> 
>      * @param lp problem
> 
>      */
> 
>     static void write_lp_solution(glp_prob lp) {
> 
>         int i;
> 
>         int n;
> 
>         String name;
> 
>         double val;
> 
>  
> 
>         name = GLPK.glp_get_obj_name(lp);
> 
>         val = GLPK.glp_get_obj_val(lp);
> 
>         System.out.print(name);
> 
>         System.out.print(" = ");
> 
>         System.out.println(val);
> 
>         n = GLPK.glp_get_num_cols(lp);
> 
>         for (i = 1; i <= n; i++) {
> 
>             name = GLPK.glp_get_col_name(lp, i);
> 
>             val = GLPK.glp_get_col_prim(lp, i);
> 
>             System.out.print(name);
> 
>             System.out.print(" = ");
> 
>             System.out.println(val);
> 
>         }
> 
>     }
> 
> }
> 
>  
> 
>  
> 
>  
> 
> Gesendet von Mail für Windows 10

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