f90: Calculate the trace of a matrix *.exe and *.out are the Windows and Linux executables.

trace.exe

trace.f90

PROGRAM trace

IMPLICIT NONE

! Declarations

INTEGER:: i, j, n, error
REAL,DIMENSION(:,:),ALLOCATABLE:: a
REAL:: tr=0.
 CHARACTER(20):: input, exiit

! Opening prints

PRINT*,
PRINT*,
PRINT*, 'This program is written by Mohammad A. Nilforooshan.'
PRINT*, 'All rights reserved.'
PRINT*, 'http://sites.google.com/site/mannprofile/'

! Ask for the input file, open and check it

PRINT*,
PRINT*,
PRINT*, 'Type the name of the input file.'
READ*, input
OPEN(UNIT=10, FILE=input, STATUS='OLD', IOSTAT=error)

IF (error/=0) THEN
    PRINT*,
    PRINT*,
    PRINT*, 'Error reading file.'
    STOP
END IF

! Ask the size of the matrix

PRINT*,
PRINT*,
PRINT*, 'Insert the size of the matrix.'
READ*, n

! Read the matrix

ALLOCATE(a(n,n))
READ(10,*) ((a(i,j),j=1,n),i=1,n)

! Estimate the trace and write it on the screen

DO i=1,n
    j=i
    tr=tr+a(i,j)
END DO

PRINT*,
PRINT*,
WRITE(*,*) 'Trace=', tr

! Finished

PRINT*,
PRINT*,
PRINT*, 'Press any key to exit.'
READ*, exiit

IF (exiit=='a') THEN
GO TO 69
END IF

69 END PROGRAM trace

trace.out