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[christyleomin]

I have a code like this:

MODULE DIRECT_METHODS_FOR_SOLUTION_OF_LINEAR_ALGEBRAIC_EQUATIONS

CONTAINS


FUNCTION CroutDecomp(AA,total_rows,total_columns,no_of_equations)

-----
-----
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,DIMENSION(100,100)::AA,x
REAL,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)


END PROGRAM LINEAR_EQUATIONS_SOLVER

Now,

On compiling, I get the following errors:


1) error 199- array AA appears in this expression as rank 1, but was declared as rank 2 (see the line in bold).

2)error 612 ':' found when not expected. Same bold line.

Can anyone tell me where I'm going wrong?

I'm new to Fortran.Sorry for a funda doubt.

Please help!

[IanLambley]

It is the format of the array subscripts. I modified the program as follows, by adding some dummy bits into the function to get it to compile without error as it did nothing in your example.

[JohnCampbell]

You appear to have only started !!

I would expect that "no_of_equations" is the key variable for you, while total_rows and total_columns only refers to the dimension of the arrays.

If you supply the arguments to "CroutDecomp (AA,total_rows,total_columns,no_of_equations) ", then I don't think you need it as a contains function.

You appear to be returning the result of the function as an array x. My apologies, while I think you can do that, I do not know how. I would convert it to a subroutine and have X as an argument.

My approach to the module would be to define the key arrays and variables you are using.
I have modified the code to remove the compile errors.
My code for crout decomposition is from memory (it's been a long time. Google to find correct code.) Hopefully it is close to what you need. the layout is close.
Hopefully this is a help. If not, then at least I've demonstrated syntax that removes some compile errors.

[christyleomin]

Thanks a lot for the reply.I'm now facing a runtime error and do not know the reason.Also, I found where is the run time error in the code below but am at no clues, why it is occuring.

Actually when j=2 and i=1, the beta(i,j) is not getting calculated- that is, the print statement for beta(i,j) is not executed when j=2 and i=1. Thouhg the program is done till j=2 and also prints i=1 but does not calculate beta(2,1) as it is not printed.

Anyone knows why?

Please help if possible!!

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
REAL aa(total_rows,total_columns)
INTEGER:: i,j,k
REAL ::sum1
REAL alpha(total_rows,total_columns),beta(total_rows,total_columns),decomposed(total_rows,total_columns)



LOOP_COLUMN:DO j=1,total_columns

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

INotEqual1:IF(i.NE.1)THEN
print*,'inside prod alpha beta',i,j
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
print*,'printing betaqqqqqqqqqqq',beta(i,j)
decomposed(i,j)=beta(i,j)
print*,'printing decomposed',decomposed(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
print *,'in CroutDecomp'



!ROW11_LOOP:DO i=1,total_rows
!COLUMN11_LOOP:DO j=1,total_columns
!PRINT*,decomposed(i,j)
!END DO COLUMN11_LOOP
!END DO ROW11_LOOP


CroutDecomp = 20

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,DIMENSION(100,100)::AA,x
REAL,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)

END PROGRAM LINEAR_EQUATIONS_SOLVER

[christyleomin]

Also, I'm just giving the following inputs:

total_rows=3
total_columns=3
no_of_equations=3

And the array AA is:

1
3
8
1
4
3
1
3
4

The above are respectively: AA(1,1),AA(1,2),AA(1,3),AA(2,1),AA(2,2),AA(2,3),AA(3,1),AA(3,2),AA(3,3)

and the b matrix is:
b(1)=4
b(2)=-2
b(3)=1

[christyleomin]

The problem is silved if i declare AA, x as below:

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

Thanks a lot everyone!