Fortran语言用杜利特尔法解线性方程组

来源：学生作业帮编辑：神马作文网作业帮分类：数学作业时间：2024/11/06 22:38:27

!LU分解法解线性方程组AX=B
!该程序从文件输入,格式为
!矩阵的维数是 3
!A矩阵
!4 2 1
!8 7 4
!16 17 15
!B矩阵
!11 34 95
PROGRAM solve_equation
REAL,DIMENSION(:,:),ALLOCATABLE::A
REAL,DIMENSION(:),ALLOCATABLE::B
CHARACTER*(80)::input = '1.txt'
INTEGER DIM
CALL GET_DIM(input,DIM)
ALLOCATE(A(DIM,DIM),B(DIM))
CALL INPUT_MATRIX(A,B,DIM,input)
CALL LU(A,DIM)
CALL solve(A,B,B,DIM)
PRINT*,B
END
SUBROUTINE GET_DIM(input,n)
CHARACTER*(*) input
CHARACTER*(80) str
INTEGER n
OPEN(10,FILE = input)
READ(10,*)str,n
CLOSE(10)
END
SUBROUTINE INPUT_MATRIX(A,B,DIM,input)
CHARACTER*(*) input
INTEGER DIM
INTEGER A(DIM,DIM),B(DIM)
OPEN(20,FILE=input)
READ(20,*)
READ(20,*)
READ(20,*) ((A(I,J),J=1,DIM),I=1,DIM)
READ(20,*)
READ(20,*) (B(I),I=1,DIM)
CLOSE(20)
END
SUBROUTINE LU(A,DIM)
INTEGER DIM
REAL A(DIM,DIM)
DO I=2,DIM
DO J=I,DIM
A(J,I-1) = A(J,I-1)*1.0/A(I-1,I-1)
m = A(J,I-1)
DO K=I,DIM
A(J,K) = A(J,K)-m*A(I-1,K)
ENDDO
ENDDO
ENDDO
END
SUBROUTINE solve(A,B,X,DIM)
INTEGER::DIM
REAL A(DIM,DIM),B(DIM),X(DIM)
!----------LY = B
DO I=2,DIM
DO J=1,I-1
B(I) = B(I) - A(I,J)*B(J)
ENDDO
ENDDO
B(DIM) = B(DIM)/A(DIM,DIM)
!---------UX=Y Y stores in B,same as X
DO I=DIM-1,1,-1
DO J=I+1,DIM
B(I) = B(I) - A(I,J)*B(J)
ENDDO
B(I) = B(I)/A(I,I)
ENDDO
END

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