wilkinson

*      matrice di wilkinson, scritto da giovanni biancuzzo

       program main
       parameter (nr=1000)
       real a(nr,nr),t1,t2
       data a/1000000*0/
       write(*,*)'Inserisci ordine matrice di wilkinson'
       read(*,*)n1
       call wilkinson(a,n1,nr)
       call stampa(a,n1,nr)
       read(*,*)n2
       do i=1,10
              t1=secnds(0.0)
              do j=1,1000
                     call wilkinson(a,n2,nr)
              enddo
              t2=secnds(t1)
              write(*,*)'Tempo impiegato: ',t2,' secondi.'
       enddo
       end

       subroutine wilkinson(a,n,nr)
       real a(nr,n)
       do i=1,n
              iflag=1
              do j=i,1,-1
                     a(i+1,j)=iflag
                     iflag=-iflag
              enddo
              a(i,n)=iflag
              a(i,i)=1
       enddo
       end

       subroutine stampa(a,n,nr)
       real a(nr,n)
       do i=1,n
       write(*,*)(a(i,j),j=1,n)
       write(*,*)
       enddo
       end