这段代码是什么意思： SUBROUTINE Weight_dble( x, Nx, xTab, NxTab, w, Ix ) INTEGER, INTENT( IN ) :: Nx, NxTab INTEGER, INTENT( OUT ) :: Ix( NxTab ) REAL (KIND=8), INTENT( IN ) :: x( Nx ), xTab( NxTab ) REAL (KIND=8), INTENT( OUT ) :: w( NxTab ) INTEGER :: L, IxTab ! Quick return if just one X value for interpolation IF ( Nx == 1 ) THEN w( 1 ) = 0.0 Ix( 1 ) = 1 RETURN ENDIF L = 1 DO IxTab = 1, NxTab ! Loop over each point for which the weights are needed ! search for index, L, such that [ x( L ), x( L+1 ) ] brackets rcvr depth DO WHILE ( xTab( IxTab ) > x( L + 1 ) .AND. L < Nx - 1 ) L = L + 1 END DO ! make note of index, L, and associated weight for interpolation Ix( IxTab ) = L w( IxTab ) = ( xTab( IxTab ) - x( L ) ) / ( x( L + 1 ) - x( L ) ) ! special code for case of a bottom following receiver !!$ IF ( w( IxTab ) /= 0.0 ) THEN !!$ Ix( IxTab ) = MIN( 2, NxTab ) ! use second depth in the mode file, or first depth if only one !!$ w( IxTab ) = 0.0 ! assert that it's a perfect match to the requested depth !!$ END IF END DO END SUBROUTINE Weight_dble

这段代码是一个子程序，名为Weight_dble，用于计算插值权重。它的输入参数包括一个实数数组x，一个整数Nx，一个实数数组xTab，一个整数NxTab，以及一个整数数组Ix。输出参数包括一个实数数组w和一个整数数组Ix。该子程序的主要功能是计算xTab中每个点的插值权重，Ix数组记录了每个点对应的x数组中的索引。具体实现方式是通过二分查找找到x数组中与xTab中每个点最接近的两个点，然后计算插值权重。如果Nx为1，则直接返回0权重和索引1。