c vectors finds the Sum , substraction, dot product and cross product
      dimension a(1,3), b(1,3) , c(1,3) , d(1,3) ,prodvec(1,3)
      pi=2.*asin(1.)
      print*,'input, ax,ay,az  '
      read*,a(1,1),a(1,2),a(1,3)
      print*,'input, bx,by,bz  '
      read*,b(1,1),b(1,2),b(1,3)
c sum and substraction
      do 10 i=1,3
      c(1,i)=a(1,i)+ b(1,i)
      d(1,i)=a(1,i)- b(1,i)
10    continue
c   dot product and angle , magnitudes
      sumdot=0.
      suma=0.
      sumb=0.
      do 20 i=1,3
      sumdot=sumdot+a(1,i)*b(1,i)
      suma=suma + a(1,i)**2
      sumb=sumb + b(1,i)**2
      if(i.eq.1)prodvec(1,i)=a(1,2)*b(1,3)-a(1,3)*b(1,2)
      if(i.eq.2)prodvec(1,i)=a(1,3)*b(1,1)-a(1,1)*b(1,3)
      if(i.eq.3)prodvec(1,i)=a(1,1)*b(1,2)-a(1,2)*b(1,1)
20    continue
      amaga=sqrt(suma)
      amagb=sqrt(sumb)
      arg=sumdot/(amaga*amagb)
      angle=acos(arg)
      print*,'magnitude of a , magn of b ,angle(deg)=',amaga,amagb,
     $ angle*180./pi
      print*,'Comp of the  Sum cx,cy,cz=',c(1,1),c(1,2),c(1,3)
      print*,'Comp of substraction dx,dy,dz=',d(1,1),d(1,2),d(1,3)
      print*,'  '
      print*,'Comp. of vector product '
      print *,(prodvec(1,i),i=1,3)
      stop
      end

RUN
 input, ax,ay,az
2.,0.,0.
 input, bx,by,bz
0.,3.,0.
 magnitude of a , magn of b ,angle(deg)=  2.  3.  90.
 Comp of the  Sum cx,cy,cz=  2.  3.  0.
 Comp of substraction dx,dy,dz=  2. -3.  0.

 Comp. of vector product
  0.  0.  6.