Fortran实现一维微分方程有限元法计算源程序

program main

!*****************************************************************************80
!
!! MAIN is the main program for FEM1D.
!
!  Discussion:
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!    FEM1D solves a one dimensional ODE using the finite element method.
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!    The differential equation solved is
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!      - d/dX (P dU/dX) + Q U  =  F
!
!    The finite-element method uses piecewise linear basis functions.
!
!    Here U is an unknown scalar function of X defined on the
!    interval [XL,XR], and P, Q and F are given functions of X.
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!    The values of U or U' at XL and XR are also specified.
!
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!    The interval [XL,XR] is "meshed" with NSUB+1 points,
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!    XN(0) = XL, XN(1)=XL+H, XN(2)=XL+2*H, ..., XN(NSUB)=XR.
!
!    This creates NSUB subintervals, with interval number 1
!    having endpoints XN(0) and XN(1), and so on up to interval
!    NSUB, which has endpoints XN(NSUB-1) and XN(NSUB).
!

!  Licensing:
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!    This code is distributed under the GNU LGPL license.
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!  Modified:
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!    01 November 2006
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!  Author:
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!    John Burkardt
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!  Parameters:
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!    real ( kind = 8 ) ADIAG(NU), the "diagonal" coefficients. 
!    That is, ADIAG(I) is the coefficient of the I-th unknown in 
!    the I-th equation.
!
!    real ( kind = 8 ) ALEFT(NU), the "left hand" coefficients.  That is, 
!    ALEFT(I) is the coefficient of the (I-1)-th unknown in the I-th equation.
!    There is no value in ALEFT(1), since the first equation
!    does not refer to a "0-th" unknown.
!
!    real ( kind = 8 ) ARITE(NU).
!    ARITE(I) is the "right hand" coefficient of the I-th
!    equation in the linear system.  ARITE(I) is the coefficient
!    of the (I+1)-th unknown in the I-th equation.  There is
!    no value in ARITE(NU) because the NU-th equation does not
!    refer to an "NU+1"-th unknown.
!