Demonstrates the difference between TR and SY prefixed BLAS calls.

TR_SY_MV.f90

! Answers discussion in the following SO question
! http://stackoverflow.com/questions/4637888/where-can-i-find-blas-example-code-in-fortran/

! Author: Matthew Rocklin
! Disclaimer: This is my first Fortran program. Please do not judge.

implicit none

integer, parameter :: N=2

real*8 :: A(N,N), x(N), y(N)

real*8 :: alpha, beta

integer :: i, j
A(1,1) = 1
A(1,2) = 1
A(2,2) = 1
x(1) = 1
x(2) = 1
y(1) = 0
y(2) = 0
alpha = 1.d0
beta = 0.d0

call dsymv('U', N, alpha, A, N, x, 1, beta, y, 1)
call dtrmv('U','N', 'N', N, A, N, x, 1)

print*, x
print*, y

end

Output

$ gfortran trsm.f90 -lblas
$ ./a.out 
   2.0000000000000000        1.0000000000000000     
   2.0000000000000000        2.0000000000000000