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[christyleomin]

I want to return an array to a function.

My program is like this:

MODULE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS
CONTAINS


FUNCTION CroutDecomp(AA,total_rows,total_columns,no_of_equations) !This routine decomposes the 'A' matrix of Ax=b into an upper and lower triangular matrix

!It is to be noted that this function fills in only the combined matrix of 'alpha's' and 'beta's' ; where alpha is the upper triangular matrix and beta is the lower triangular matrix.


!Crout's decomposition carries out 2 steps:
!1) First, for i=1,2,---,j use , beta(i,j)= a(i,j)-(summation over k=1 to i-1)[alpha(i,k)*beta(k,j)
!2)Second, for i=j+1,--N use, alpha(i,k)= 1/beta(j,j)*((a(i,j)-summation over k=1 to j-1 [ alpha(i,k)*beta(k,j)]


INTEGER::total_rows,total_columns ,no_of_equations

INTEGER:: i,j,k
REAL ::sum1
REAL*8 alpha(total_rows,total_columns),beta(total_rows,total_columns),decomposed(total_rows,total_columns)
REAL*8,DIMENSION(100,100)::AA,x


!!!The program calculates a 3 x 3 array 'decomposed'CroutDecomp = decomposed

END FUNCTION CroutDecomp




END MODULE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS


PROGRAM LINEAR_EQUATIONS_SOLVER
USE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS
!IMPLICIT NONE
REAL*8,DIMENSION(100,100)::AA,x
REAL*8,DIMENSION(100)::b
INTEGER::total_rows,total_columns,no_of_equations,i,j
PRINT*, 'ENTER THE TOTAL NUMBER OF ROWS AND COLUMNS'
READ*, total_rows,total_columns
PRINT*, 'ENTER THE TOTAL NUMBER OF EQUATIONS'
READ*, no_of_equations
PRINT*, 'ENTER THE A MATRIX OF Ax = b'
ROW_LOOP:DO i=1,total_rows
COLUMN_LOOP:DO j=1,total_columns
READ*,AA(i,j)
END DO COLUMN_LOOP
END DO ROW_LOOP
PRINT*, 'ENTER THE b MATRIX OF Ax = b'
ROW_LOOP:DO i=1,total_rows
READ*,b(i)
END DO ROW_LOOP

x= CroutDecomp(AA,total_rows,total_columns,no_of_equations)

!!!I dont get the array calculated above retruned here.Pls can anyone help?



END PROGRAM LINEAR_EQUATIONS_SOLVER

[christyleomin]

I shall be grateful if someone can help.Im stuck because of this!

[DrTip]

OK

thing is do you really want to have a function return an array. I mean really really really.

you can do it using but you have to have an interface defined. I use these so rarely that i can never remember the syntax. So I will leave you to look it up

someting like

[christyleomin]

Thanks, I was looking at the bottom-most thread in this post:

http://www.tek-tips.com/viewthread.cfm?qid=1516435

Not able to get what he does? Any help will be appreciated? There is no mennton of interface used in this.

[christyleomin]

I did try defining an interface but get a run time error:

MODULE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS
CONTAINS

FUNCTION CroutDecomp(AA,total_rows,total_columns,no_of_equations) !This routine decomposes the 'A' matrix of Ax=b into an upper and lower triangular matrix

!It is to be noted that this function fills in only the combined matrix of 'alpha's' and 'beta's' ; where alpha is the upper triangular matrix and beta is the lower triangular matrix.


!Crout's decomposition carries out 2 steps:
!1) First, for i=1,2,---,j use , beta(i,j)= a(i,j)-(summation over k=1 to i-1)[alpha(i,k)*beta(k,j)
!2)Second, for i=j+1,--N use, alpha(i,k)= 1/beta(j,j)*((a(i,j)-summation over k=1 to j-1 [ alpha(i,k)*beta(k,j)]

interface

REAL*8 CroutDecomp(100,100)

end interface





INTEGER::total_rows,total_columns ,no_of_equations

INTEGER:: i,j,k
REAL ::sum1
REAL*8 alpha(total_rows,total_columns),beta(total_rows,total_columns),decomposed(total_rows,total_columns)
REAL*8,DIMENSION(100,100)::AA,x


LOOP_COLUMN:DO j=1,total_columns

LOOP_ROWS:DO i= 1,j
print*,'inside i', i
alpha(i,i)=1
sum1=0

INotEqual1:IF(i.NE.1)THEN

LOOP_PROD_ALPHA_BETA:DO k=1,i-1
sum1=sum1+(alpha(i,k)*beta(k,j))
END DO LOOP_PROD_ALPHA_BETA
END IF INotEqual1

beta(i,j)=AA(i,j)-sum1
decomposed(i,j)=beta(i,j)

END DO LOOP_ROWS



jLessThanNoOfEqns:IF(j.LT.no_of_equations)THEN
LOOP_ROWS_1: DO i=j+1,no_of_equations
sum1=0

jNotEqual1:IF(j.NE.1)THEN
LOOP_PROD_ALPHA_BETA2:DO k=1,j-1
sum1=sum1+(alpha(i,k)*beta(k,j))
END DO LOOP_PROD_ALPHA_BETA2
END IF jNotEqual1

alpha(i,j)=(1/beta(j,j))*(AA(i,j)-sum1)
decomposed(i,j)=alpha(i,j)
END DO LOOP_ROWS_1

END IF jLessThanNoOfEqns

END DO LOOP_COLUMN

CroutDecomp=decomposed(1:total_rows,1:total_columns)




END FUNCTION CroutDecomp




END MODULE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS


PROGRAM LINEAR_EQUATIONS_SOLVER
USE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS
!IMPLICIT NONE
REAL*8,DIMENSION(100,100)::AA,x
REAL*8,DIMENSION(100)::b
INTEGER::total_rows,total_columns,no_of_equations,i,j
PRINT*, 'ENTER THE TOTAL NUMBER OF ROWS AND COLUMNS'
READ*, total_rows,total_columns
PRINT*, 'ENTER THE TOTAL NUMBER OF EQUATIONS'
READ*, no_of_equations
PRINT*, 'ENTER THE A MATRIX OF Ax = b'
ROW_LOOP:DO i=1,total_rows
COLUMN_LOOP:DO j=1,total_columns
READ*,AA(i,j)
END DO COLUMN_LOOP
END DO ROW_LOOP
PRINT*, 'ENTER THE b MATRIX OF Ax = b'
ROW_LOOP:DO i=1,total_rows
READ*,b(i)
END DO ROW_LOOP

x= CroutDecomp(AA,total_rows,total_columns,no_of_equations)

ROW11_LOOP:DO i=1,total_rows
COLUMN11_LOOP:DO j=1,total_columns
PRINT*,'now', x(i,j)
END DO COLUMN11_LOOP
END DO ROW11_LOOP

END PROGRAM LINEAR_EQUATIONS_SOLVER

[christyleomin]

Dear Dr.Tip,

Please can you guide?YEs, I need to return an array rather than using sub routine.

I want to group all functions in a module (like a C++ class) and if I use sub routine I will have to remove it from MODULE.

The return of the array will help me to great extent.

[IanLambley]

Just insert the name of the array into the function parameter list, having dimensioned it in the main program and it will be returned updated. the return value of the function can be the status:
Example: