| 1 | module interp_line_mod |
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| 2 | |
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| 3 | implicit none |
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| 4 | |
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| 5 | contains |
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| 6 | |
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| 7 | subroutine interp_line(x1,y1,len1,x2,y2,len2) |
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| 8 | implicit none |
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| 9 | !----------------------------------------------------------------------- |
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| 10 | ! |
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| 11 | ! Purpose: Do a series of linear interpolations |
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| 12 | ! Data sets are organized as vectors (see below) |
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| 13 | ! If x2(:), and abscissa at which interpolation is requiered, lies |
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| 14 | ! outside of the interval covered by x1(:), instead of doing an |
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| 15 | ! extrapolation, y2() is set to the value y1() corresponding to |
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| 16 | ! the nearby x1(:) point |
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| 17 | ! |
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| 18 | c----------------------------------------------------------------------- |
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| 19 | ! arguments |
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| 20 | ! --------- |
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| 21 | ! inputs: |
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| 22 | real,intent(in) :: x1(len1) ! ordered list of abscissas |
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| 23 | real,intent(in) :: y1(len1) ! values at x1(:) |
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| 24 | integer,intent(in) :: len1 ! length of x1(:) and y1(:) |
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| 25 | real,intent(in) :: x2(len2) !ordered list of abscissas at which interpolation is done |
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| 26 | integer,intent(in) :: len2 ! length of x2(:) and y2(:) |
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| 27 | ! outputs: |
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| 28 | real,intent(out) :: y2(len2) ! interpolated values |
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| 29 | !----------------------------------------------------------------------- |
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| 30 | |
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| 31 | ! local variables: |
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| 32 | integer i,j |
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| 33 | |
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| 34 | |
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| 35 | do i=1,len2 |
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| 36 | ! check if x2(i) lies outside of the interval covered by x1() |
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| 37 | if(((x2(i).le.x1(1)).and.(x2(i).le.x1(len1))).or. |
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| 38 | & ((x2(i).ge.x1(1)).and.(x2(i).ge.x1(len1)))) then |
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| 39 | ! set y2(i) to y1(1) or y1(len1) |
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| 40 | if (abs(x2(i)-x1(1)).lt.abs(x2(i)-x1(len1))) then |
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| 41 | ! x2(i) lies closest to x1(1) |
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| 42 | y2(i)=y1(1) |
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| 43 | else |
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| 44 | ! x2(i) lies closest to x1(len1) |
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| 45 | y2(i)=y1(len1) |
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| 46 | endif |
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| 47 | |
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| 48 | else |
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| 49 | ! find the nearest neigbours and do a linear interpolation |
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| 50 | do j=1,len1-1 |
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| 51 | if(((x2(i).ge.x1(j)).and.(x2(i).le.x1(j+1))).or. |
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| 52 | & ((x2(i).le.x1(j)).and.(x2(i).ge.x1(j+1)))) then |
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| 53 | y2(i)=((x2(i)-x1(j))/(x1(j+1)-x1(j)))*y1(j+1)+ |
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| 54 | & ((x2(i)-x1(j+1))/(x1(j)-x1(j+1)))*y1(j) |
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| 55 | endif |
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| 56 | enddo |
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| 57 | endif |
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| 58 | |
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| 59 | enddo |
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| 60 | |
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| 61 | end subroutine interp_line |
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| 62 | |
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| 63 | end module interp_line_mod |
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