Reading and Multiplying Matrices in Fortran?

[Clint_Johnson]

I have two files I need to read arrays out of using the "open" command and I keep getting a compiler error saying "(col. 1) remark: LOOP WAS VECTORIZED." I assume this is because I am reading the data out of the files incorrectly but I don't really understand what "loop was vectorized" means. The data in the files is formatted as
IxJ
number
number
number
...

where I and J are the dimensions the array and number represents numbers in the array

Here's what I have although I am pretty sure my error lies in my reading of the array

PROGRAM MAT_MUL_FORTRAN_INTRINSIC_FUNC
IMPLICIT NONE
CHARACTER(LEN=30) :: INPUT_FILE_1, INPUT_FILE_2
REAL, DIMENSION(10000,10000) :: DATA_ARRAY_1, DATA_ARRAY_2, DATA_ARRAY_3

PRINT *, "PLEASE ENTER THE COMPLETE NAME OF THE TWO FILES CONTAINING THE MATRICES YOU WISH TO MULTIPLY"
READ *, INPUT_FILE_1, INPUT_FILE_2

OPEN(1, FILE=INPUT_FILE_1, ACTION="READ", FORM='FORMATTED')
READ(1) DATA_ARRAY_1
CLOSE(1)

OPEN(2, FILE=INPUT_FILE_1, ACTION="READ", FORM='FORMATTED')
READ(2) DATA_ARRAY_2
CLOSE(2)

DATA_ARRAY_3 = DATA_ARRAY_1*DATA_ARRAY_2

OPEN(3, FILE="RESULTING_MATRIX.dat", ACTION="WRITE", FORM='FORMATTED')
WRITE(3) DATA_ARRAY_3
CLOSE(3)

END PROGRAM MAT_MUL_FORTRAN_INTRINSIC_FUNC

Thanks in advance for the help!

Homework Equations

The Attempt at a Solution

 

[Valkarie]

The problem is that you are not reading the data from your files correctly. You need to use a loop to read in each element of the array from the file. For example:PROGRAM MAT_MUL_FORTRAN_INTRINSIC_FUNCIMPLICIT NONECHARACTER(LEN=30) :: INPUT_FILE_1, INPUT_FILE_2REAL, DIMENSION(10000,10000) :: DATA_ARRAY_1, DATA_ARRAY_2, DATA_ARRAY_3PRINT *, "PLEASE ENTER THE COMPLETE NAME OF THE TWO FILES CONTAINING THE MATRICES YOU WISH TO MULTIPLY"READ *, INPUT_FILE_1, INPUT_FILE_2OPEN(1, FILE=INPUT_FILE_1, ACTION="READ", FORM='FORMATTED')DO i = 1, 10000 DO j = 1, 10000 READ(1,*) DATA_ARRAY_1(i,j) END DOEND DOCLOSE(1)OPEN(2, FILE=INPUT_FILE_1, ACTION="READ", FORM='FORMATTED')DO k = 1, 10000 DO l = 1, 10000 READ(2,*) DATA_ARRAY_2(k,l) END DOEND DOCLOSE(2)DATA_ARRAY_3 = DATA_ARRAY_1*DATA_ARRAY_2OPEN(3, FILE="RESULTING_MATRIX.dat", ACTION="WRITE", FORM='FORMATTED')DO m = 1, 10000 DO n = 1, 10000 WRITE(3,*) DATA_ARRAY_3(m,n) END DOEND DOCLOSE(3)END PROGRAM MAT_MUL_FORTRAN_INTRINSIC_FUNC

 

[Mene]

I understand your frustration with getting a compiler error and not fully understanding what it means. In this case, the error message "loop was vectorized" means that the compiler has automatically optimized your code by converting the loop to a vector operation. This is usually a good thing and can improve the performance of your code. However, it is possible that the way you are reading the arrays is not compatible with vectorization, which is why you are getting the error.

Looking at your code, it seems like you are trying to read the entire data file into a single array. However, the data in your files is formatted as a matrix, with the dimensions I and J specified at the top. This means you need to read the data into a 2D array, with I rows and J columns. Here is a possible solution for reading the data:

PROGRAM MAT_MUL_FORTRAN_INTRINSIC_FUNC
IMPLICIT NONE
CHARACTER(LEN=30) :: INPUT_FILE_1, INPUT_FILE_2
REAL, DIMENSION(:,:), ALLOCATABLE :: DATA_ARRAY_1, DATA_ARRAY_2, DATA_ARRAY_3
INTEGER :: I, J

PRINT *, "PLEASE ENTER THE COMPLETE NAME OF THE TWO FILES CONTAINING THE MATRICES YOU WISH TO MULTIPLY"
READ *, INPUT_FILE_1, INPUT_FILE_2

OPEN(1, FILE=INPUT_FILE_1, ACTION="READ", FORM='FORMATTED')
READ(1,*) I, J ! Read the dimensions of the array
ALLOCATE(DATA_ARRAY_1(I,J)) ! Allocate the array with the correct dimensions
READ(1,*) DATA_ARRAY_1 ! Read the data into the array
CLOSE(1)

OPEN(2, FILE=INPUT_FILE_2, ACTION="READ", FORM='FORMATTED') ! Note: changed to INPUT_FILE_2
READ(2,*) I, J
ALLOCATE(DATA_ARRAY_2(I,J))
READ(2,*) DATA_ARRAY_2
CLOSE(2)

DATA_ARRAY_3 = DATA_ARRAY_1*DATA_ARRAY_2

OPEN(3, FILE="RESULTING_MATRIX.dat", ACTION="WRITE", FORM='FORMATTED')
WRITE(3,*) DATA_ARRAY_3
CLOSE(3)

END PROGRAM MAT_MUL_FORTRAN_INTRINSIC_FUNC

This code reads the dimensions of the array from the first line of the file, allocates the array with the