Returning an array

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 REAL8 alpha(total_rows,total_columns),beta(total_rows,total_columns),decomposed(total_rows,total_columns) REAL8,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 REAL8,DIMENSION(100,100)::AA,x REAL8,DIMENSION(100)b INTEGERtotal_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

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

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

functon foo (a)
interface 
  real(:) foo
  real a 
end interface

   foo = ....
end function

I am not going to look it up because I think thats enough of a steer for you

The reason that I hardly ever use them is that is a non standard fortran coding pattern.

usually a subroutine is used and the call code handles the array sizing etc

subroutine subs (a , b)
real a 
real(:) b 

b(1) = a
b(2) = a
b(3) = a 

end subroutine 

program main

real(3) test

call subs (4,test)

end program

[/code]

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.

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 REAL8 alpha(total_rows,total_columns),beta(total_rows,total_columns),decomposed(total_rows,total_columns) REAL8,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 REAL8,DIMENSION(100,100)::AA,x REAL8,DIMENSION(100)b INTEGERtotal_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

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.

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:

dimension a(100,100),b(100)
isize = 100
j=1
do while(j .lt. 200)
  i=myfunction(a,isize,j,b)

  if(i.eq. 0)then
    Print *,'success for j=',j
    Print *,(b(k),k=1,isize)
  else
    Print *,'requested column outside range of input array j=',j
  endif
  j=j+50
enddo
end
integer function myfunction(aa,iisize,jj,bb)
dimension a(iisize,iisize), b(iisize)
if( jj .lt. 1 .or. jj .gt. iisize)then
! failure
  myfunction = 1
else
! success
  myfunction = 0
  do i=1,iisize
    bb(i) = aa(jj,i)
  enddo
endif
end

Note the indenting to make it readable. When you post code, press the 'Code' keyword before and after the insertion of the code and indenting will be retained. Oh, and please don't mention C++ again, it scares me something rotten! Regards Ian