! orthog - Program to test if a pair of vectors
! is orthogonal. Assumes vectors are in 3D space
program orthog
!* Initialize the vectors a and b
integer*4 i
real*8 a(3), b(3), a_dot_b
write(*,*) 'Enter the first vector'
do i=1,3
write(*,*) ' a(', i, ') = '
read(*,*) a(i)
enddo
write(*,*) 'Enter the second vector'
do i=1,3
write(*,*) ' b(', i, ') = '
read(*,*) b(i)
enddo
!* Evaluate the dot product as sum over products of elements
a_dot_b = 0.0
do i=1,3
a_dot_b = a_dot_b + a(i)*b(i)
enddo
!* Print dot product and state whether vectors are orthogonal
if( a_dot_b .eq. 0.0 ) then
write(*,*) 'Vectors are orthogonal'
else
write(*,*) 'Vectors are NOT orthogonal'
write(*,*) 'Dot product = ', a_dot_b
endif
stop
end