Calculate the Sum of Two Vectors

This is a part of the student software manual project for Math 5610: Computational Linear Algebra and Solution of Systems of Equations.

Routine Name: vec_add

Author: Christian Bolander

Language: Fortran. This code can be compiled using the GNU Fortran compiler by

$ gfortran -c vec_add.f90

and can be added to a program using

$ gfortran program.f90 vec_add.o

Description/Purpose: This routine will add two vectors, a and b, together and find the sum, a vector c.

Input:

n : INTEGER - the length of the vectors being added together

a : REAL - an arbitrary vector of length n

b : REAL - an arbitrary vector of length n

Output:

c : REAL - the sum of a and b

Usage/Example:

This routine can be implemented in a program as follows

n = 8
ALLOCATE(a(1:n), b(1:n), c(1:n))
DO i = 1, n
	a(i) = i
	b(i) = i + 1
END DO
CALL vec_add(a, b, c, n)
DO i = 1, n
	WRITE(*,*) c(i)
END DO

The output from the above code:

   3.0000000000000000     
   5.0000000000000000     
   7.0000000000000000     
   9.0000000000000000     
   11.000000000000000     
   13.000000000000000     
   15.000000000000000     
   17.000000000000000 

which is the vector c.

Implementation/Code: The code for vec_add can be seen below.

SUBROUTINE vec_add(a, b, c, n)
IMPLICIT NONE

INTEGER, INTENT(IN) :: n
REAL*8, INTENT(IN) :: a(1:n), b(1:n)
REAL*8, INTENT(OUT) :: c(1:n)
INTEGER :: i

! Add two vectors together element-wise.
DO i = 1, n
	c(i) = a(i) + b(i)
END DO
END SUBROUTINE