Re: [Help-glpk] java glpk

[Heinrich Schuchardt]

Hello David,

GLPK for Java is  a JNI wrapper library generated with SWIG around the GLPK C
library.

Your first point of reference should be file
glpk-4.47/doc/glpk.pdf
of the GLPK source distribution available at
ftp://ftp.gnu.org/gnu/glpk/glpk-4.47.tar.gz

In chapter 2.2.12 you will find the description of function
void glp_set_mat_row(glp_prob *lp, int i, int len,
const int ind[], const double val[]);

Some information is available in the javadoc that is generated
when building GLPK for Java and additionally available online at
http://glpk-java.sourceforge.net/apidocs/index.html

Please, also have a look at the examples in directory
glpk-java-1.0.22/examples/java
of the GLPK for Java source which you can download from
http://glpk-java.sourceforge.net

A further point of reference is the GLPK wikibook at
http://en.wikibooks.org/wiki/GLPK

Please, do not hesitate to contact me if further questions remain.

If you are looking for a less complex API to call GLPK you may want
to have a look at my project at
http://www.xypron.de/projects/linopt/

Best regards

Heinrich Schuchardt

-------- Original-Nachricht --------
> Datum: Mon, 7 Jan 2013 18:42:40 +0100
> Betreff: [Help-glpk] java glpk

> Hi,
> 
> It is the first I am using GLPK, and I should integrate it to my Java
> project.
> I succeed to install it in linux environment and I start reading some code
> source examples (only 2 examples availbale in the official documentation).
> I have some questions about setting constraints (columns).
> In fact, I want to know why we should use integer array and double array ?
> What is their lenght (is it constraint number) ?
> Shall I use an array for each constraint (column) ?
> Which values should be used to set the table ?
> What is the importance of this statment ? :
>         GLPK.glp_set_mat_row(lp, 1, 2, ind, val);
> What are the 2nd and the 3rd parameters of this function ?
> 
> I am looking for your help !
> Thanks in advance.
> Regards,
> 
> ///The example I am speaking about : It is available at the official
> documentation of java-glpk
> 
> // Minimize z = (x1-x2) /2 + (1-(x1-x2)) = -.5 * x1 + .5 * x2 + 1
>         // subject to
>         // 0.0<= x1 - x2 <= 0.2
>         // where,
>         // 0.0 <= x1 <= 0.5
> 
> 
>         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 columns
>         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, .5);
>         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, .5);
>         // Create constraints
>         GLPK.glp_add_rows(lp, 1);
>         GLPK.glp_set_row_name(lp, 1, "c1");
>         GLPK.glp_set_row_bnds(lp, 1, GLPKConstants.GLP_DB, 0, 0.2);
>         ind = GLPK.new_intArray(3);
>         GLPK.intArray_setitem(ind, 1, 1);
>         GLPK.intArray_setitem(ind, 2, 2);
>         val = GLPK.new_doubleArray(3);
>         GLPK.doubleArray_setitem(val, 1, 1.);
>         GLPK.doubleArray_setitem(val, 2, -1.);
>         GLPK.glp_set_mat_row(lp, 1, 2, ind, 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);
>         // 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();
>         }
>         }
>         /**
>         * 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);
>         }
>   }