!*****************************************************
!*  This program multiplies a polynomial P(x) by a   *
!*  polynomial Q(x)                                  *
!* ------------------------------------------------- *
!* Ref.: "Mathématiques en Turbo-Pascal By M. Ducamp *
!* and A. Reverchon (vol 2), Eyrolles, Paris, 1988"  *
!* [BIBLI 05].                                       * 
!* ------------------------------------------------- *
!* SAMPLE RUN:                                       *
!*                                                   *
!* MULTIPLY TWO POLYNOMIALS:                         *
!*                                                   *
!* P(X) = 'x3 - 6x + 7'                              *
!* Q(x) = '5x5 -3x4 +x2 -3'                          *
!*                                                   *
!*+      5X8 -     3X7 -    30X6 +    54X5 -    21X4 *
!*-      9X3 +     7X2 +    18X -    21              *
!*                                                   *
!* ------------------------------------------------- *
!* Functions used (of module Polynoms):              *
!*                                                   *
!*  AddNumber(), EnterPolynom(), DisplayPolynom()    *
!*  and MultNumber().                                *
!*                                                   *
!*                       F90 version by J-P Moreau.  *
!*                           (www.jpmoreau.fr)       *
!*****************************************************
PROGRAM MULTPOL
Use Polynoms

type(ar_polynom)  P,Q

  print *,''
  print *,'MULTIPLY TWO POLYNOMIALS:'
  print *,''
  if (EnterPolynom(' P(X) = ', P).eq.0) stop
  if (EnterPolynom(' Q(X) = ', Q).eq.0) stop
  print *,''
  if (MultPolynom(P,Q,Q).ne.0) then
    call DisplayPolynom(Q)
  else
    print *,' Error in multiplication.'
  end if
  print *,''
  print *,''
  stop
END


  ! P(X) * Q(X) = R(X)
  integer Function MultPolynom(P,Q,R1)
  USE POLYNOMS
    type(ar_polynom) P,Q,R,R1
    type(ar_number)  u
    R%degree=0                !set R polynomial to zero
	do i=0, AR_MAXPOL
      R%coeff(i)%value=0
	  R%coeff(i)%p=0
      R%coeff(i)%q=1
	end do
    !verify that P and Q are not void
    if (P%degree.eq.0.and.P%coeff(0)%value.eq.0) then 
	  MultPolynom=0
	  return
    end if
    if (Q%degree.eq.0.and.Q%coeff(0)%value.eq.0) then 
	  MultPolynom=0
	  return
    end if
    R%degree=P%degree+Q%degree
	
    if (R%degree>AR_MAXPOL) then     !R degree is too big
	  MultPolynom=0
	  return
	end if
    do n=0, R%degree
      if (SetNumber(R%coeff(n),'0').eq.0) then
	    MultPolynom=0
	    return
	  end if
      do i=0, P%degree
        j=n-i
        if (j>=0.and.j<=Q%degree) then
          if (MultNumber(P%coeff(i),Q%coeff(j),u).eq.0) then
	        MultPolynom=0
	        return
		  end if
          if (AddNumber(R%coeff(n),u,R%coeff(n)).eq.0) then
	        MultPolynom=0
	        return
		  end if
        end if
      end do
    end do
    MultPolynom=1
	R1=R
  End


!end of file multpol.f90