Using functions in Java

[Sattiraju Prabhakar]

Hi,

I am trying to use Scilab (5.1.1) from a Java (jdk 6 update 13) application. 
I have been experimenting with some Scilab scripts that use
function ("function" and "deff") definitions. 
When I tried to convert these scripts into Java, I have come
across a number of problems. 

Problems using "function"
================

I took the "function percentile" declaration from Professor Gilberto Gurroz's
Basic Statistics and Probability using Scilab. I reproduce below the script.

function [p] = percentile(x,r)
//This function calculates the 100*r-th percentile
//(0<r<1) for the vector x
xx = gsort(x);
[n m] = size(xx);
if m>n & n == 1 
   n = m;
end 
if r<0 | r>1 then
   disp('Percentile value must be between 0 and 1');
else
   k = n*r;
   if k-floor(k) ~= 0  
      p = xx(round(n*r));
   else
      p = (xx(k)+xx(k+1))/2;
   end
end

It is used as follows
Q1 = percentile(x,0.25)

I tried to put it in Java code in two different ways. 

A. In the first attempt, I tried to execute each line using
Scilab.Exec. The code follows.

 public void percentile() {
        Scilab.Exec("function [p] = percentile(x,r)");
//This function calculates the 100*r-th percentile
//(0<r<1) for the vector x
        Scilab.Exec("xx = gsort(x);");
        Scilab.Exec("[n m] = size(xx);");
        Scilab.Exec("if m>n & n == 1");
        Scilab.Exec("n = m;");
        Scilab.Exec("end");
        Scilab.Exec("if r<0 | r>1 then");
        Scilab.Exec("disp('Percentile value must be between 0 and 1');");
        Scilab.Exec("else");
        Scilab.Exec("k = n*r;");
        Scilab.Exec(" if k-floor(k) ~= 0");
        Scilab.Exec("p = xx(round(n*r)); ");
        Scilab.Exec("else");
        Scilab.Exec("p = (xx(k)+xx(k+1))/2;");
        Scilab.Exec("end");
        Scilab.Exec("endfunction");
  }

I tried to apply this function as follows.
SciDouble Q1P = new SciDouble("Q1");
 Scilab.Exec("Q1 = percentile(x,0.25)");    
        Q1P.Get();
        Q1P.disp();

I get the following error. 
double Q1=
 
    0.  
Error in Java_javasci_Scilab_Exec routine.

B. I tried to declare the entire function as a string and pass the
string as argument to Scilab.Exec().


public void percentile() {
     String perc2 = "function [p] = percentile(x,r) \n xx = gsort(x); \n [n m] = size(xx); \n if m>n & n == 1 \n n = m; \n end \n if r<0 | r>1 then \n disp('Percentile value must be between 0 and 1'); \n else \n k = n*r; \n if k-floor(k) ~= 0 \n p = xx(round(n*r)); \n else \n p = (xx(k)+xx(k+1))/2; \n end \n endfunction";
    Scilab.Exec(perc2);
}

I tried it without \n, and later with \n. In both cases, I got the same error as above. 

I also tried Java conversion of a simpler script, with the same result


//inline definition (see function)
function [x,y]=myfct(a,b)
x=a+b
y=a-b
endfunction

public void myFunction(){
        Scilab.Exec("function [x,y]=myfct(a,b)");
        Scilab.Exec("x=a+b");
        Scilab.Exec("y=a-b");
        Scilab.Exec("endfunction"); 
    }

     public void myFunction2(){
         String fun = "function [x,y]=myfct(a,b)  x=a+b  y=a-b  endfunction";
        Scilab.Exec(fun);
    }

2. Using deff
=============

I was able to successfully write and execute the above example using deff

Scilab.Exec("deff('[x,y]=myfct(a,b)', ['x=a+b'; 'y=a-b'])");

"deff" requires that we state the "statements" of the function as matrix of strings. 
If you have a String inside the function declaration (of Scilab script), as in percentile, then
it becomes a problem.

I was not able to get a correct result for percentile using deff and Java. 
Here is my code:
Scilab.Exec("deff('[p]=percentile(x,r)', ['xx = gsort(x);'; '[n m] = size(xx);'; ' if m>n & n == 1  n = m;'; 'end'; 'if r<0 | r>1 then disp('Percentile value must be between 0 and 1');' ; 'else  k = n*r;'; 'if k-floor(k) ~= 0  p = xx(round(n*r));'; 'else  p = (xx(k)+xx(k+1))/2;'; 'end' ])");

I would like to end with a general question. Each of the above methods takes some effort. 
If the function definition is long, then the effort needed to convert into Java code can be
substantial. Is there a simple method?

Thanks,
Prabhakar
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