facing the problem in line no.... F(j)>0.0 in this loop

 if F(j)>0.0
          a=rand();
          if a>0.5
              w=1;
          else
              w=0;
          end
          if w==1
              i=i+1;
              sel1(i)=j;
              m1(i)=sel1(i);
              F(j)=F(j)-1;
          else
          end
      else
      end
  end
end

[John D'Errico]

What problem?

I do wonder why you think EVERY if statement must have a blank else clause. But that is not at all relevant. You also have far more end statements in this code to ever run.

If you have an error message, then give us the ENTIRE text of the message, not just part of the message. Provide the complete error as generated.