Self study guide: Fortran 95 - University of Cambridge

1.9 The stop statement
We have just seen how the exit command can be used to terminate a do loop. If
you wish execution of your program to cease, you can insert a stop statement; this
can incorporate some text, which is output when your program halts and identifies
where this happened, e.g.
1.10 Arrays
stop ’this is where it all ends up’
A great deal of scientific computation involves the manipulation of vectors, matrices
and more general arrays of numbers. In F95 we can have an array of variables set up
in the declarations statements.
How do we specify arrays? The simplest way is to give the dimension in parentheses.
real :: a(3) ! a is an array of 3 values: a vector
real :: m(3,3) ! m is a rank 2 array: a matrix
We call the part in parentheses a shape. Each element of the array can be addressed
in the program using a similar notation. Here is a simple example:
program vector
implicit none
real :: v(3)
real :: x
integer :: i
v(1) = 0.25
v(2) = 1.2
v(3) = 0.2
! compute the modulus squared of the vector
x = 0.0
do i=1,3
x = x + v(i)*v(i)
end do
write(*,*) ’Modulus squared = ’,x
end program vector
Notice how we use a loop to compute the sum over all elements of the vector.
A second example will show us how we can implement simple vector and matrix
operations:
17