Vector Magic and Naming Conventions for Fortran

[ShoxPhysics]

I have just about finished this program, I only need to calculate my velocity. I think that this velocity should be calculated by taking the value from the 4th column of my data set here:https://docs.google.com/file/d/0BzuDEPd26OcheVhiWlZ3STlZU0k/edit?usp=sharing which have called ivar_3 and multiplying it by the difference of the 1st column in the line of the value and the line preceding it. Is this thought process correct? I have done the following (code I am talking about is in blue), can somebody tell me where I might be going wrong because it will not compile?

program WSUPhys_csv
  implicit none

  integer :: stat, num_lines, ivar1, ivar2, ivar3, &
             MaxVert,MaxSide,MaxForward
  real :: rvar, Sum_ivar1, Sum_ivar2, Sum_ivar3, & 
          Avg_ivar1, Avg_ivar2, Avg_ivar3, Vel, SumVel, MaxVel
  character*80 :: line
  logical :: err
  
  err = .false.

  write(*,*) "Reading file..."

  ! open input file
  open(10,file='DATA-002.csv',status='old',iostat=stat)
  if (stat .ne. 0) then
    err = .true.
    write(*,*) 'File cannot be opened !'
    go to 99   
  end if

  num_lines = 0
  Sum_ivar1 = 0
  Sum_ivar2 = 0
  Sum_ivar3 = 0
  MaxVert=0
  MaxSide=0
  MaxForward=0
  SumVel=0
  MaxVel=0
  do
    read(10,'(A)',end=99, iostat=stat) line 
    if (stat .ne. 0) then
      err = .true.
      write(*,*) 'Error reading data !'
      go to 99
    end if
    ! skip comment/header lines beginning with ";"
    if (adjustl(trim(line(1:1))) .eq. ';') then
      cycle
    end if
    ! read string line into numeric variables
    read(line,*) rvar, ivar1, ivar2, ivar3
    num_lines = num_lines + 1    
    if (num_lines <=  10) then
      write(*,*) num_lines, ':', rvar, ivar1, ivar2, ivar3
    end if
    Sum_ivar1 = Sum_ivar1 + ABS(ivar1) 
    Sum_ivar2 = Sum_ivar2 + ABS(ivar2) 
    Sum_ivar3 = Sum_ivar3 + ABS(ivar3)
    Vel=(ABS(ivar_3))*(rvar-rvar)
    SumVel=SumVel+ ABS(Vel)
    If (ABS(ivar1) > MaxVert) then
      MaxVert=ivar1
    end if
    If (ABS(ivar2) > MaxSide) then
      MaxSide=ivar1
    end if
    If (ABS(ivar3) > MaxForward) then
      MaxForward=ivar1
    end if   
    If (Vel > MaxVel) then
      MaxVel=Vel
  end do
  ! close file
  99 continue
  close (10)

  ! when file processing OK
  if (.not. err) then
    write(*,*) '...done.'
    ! compute averages
    Avg_ivar1 = (Sum_ivar1 / num_lines)
    Avg_ivar2 = (Sum_ivar2 / num_lines)
    Avg_ivar3 = (Sum_ivar3 / num_lines)
    AvgVel = (SumVel / num_lines)
    !

    write(*,*) 'Lines processed: ', num_lines
    write(*,*) 'Average vertical acceleration', Avg_ivar1
    write(*,*) 'Average sideways acceleration', Avg_ivar2
    write(*,*) 'Average forwards acceleration', Avg_ivar3
    write(*,*) 'Maximum vertical acceleration', MaxVert
    write(*,*) 'Maximum sideways acceleration', MaxSide
    write(*,*) 'Maximum forward acceleration ',  MaxForward
    write (*,*) 'Average forward velocity', AvgVel
    write (*,*) 'Maximum velocity', MaxVel
  end if  
end program WSUPhys_csv

 

[AlephZero]

You have an "implicit none" statement which means you have to declare all the variables you use.

You haven't declared SumVel and MaxVel.

There may be more errors, but that's a start.

 

[Solkar]

In addition to AlphaZero's remark:

Sum_ivar1 = 0
Sum_ivar2 = 0
Sum_ivar3 = 0
MaxVert=0
MaxSide=0
MaxForward=0

Ouch!

Fortran is sort-of a short for Formula Translating and it has that name for a reason - namely for providing means for easy translation of mathematical calculus into a form understandable by machines.

So - what would it be good for if it would not provide means to deal with basic algebraic concepts like vectors and matrices?

Instead of stepping line-by-line through this I've compiled a little snippet from which you may take some concepts for improving readability and structure of your code.

!----------------------------------------------------------------------------80
!> @file vector_demo.f90
!> @brief illustrating some basic Fortran vector magic, useful practices 
! and proposes a consistent naming convention
!> @author Solkar
!------------------------------------------------------------------------------

!------------------------------------------------------------------------------
!> @function vector_demo
!> @brief entry point, main routine
!------------------------------------------------------------------------------
program vector_demo
    implicit none
    !- parameters ("constants" in C) in mulit-char CAPS,
    integer,                        parameter :: RKIND = 8      ! precision
    !- ... everything else (except matrices) small,
    real(kind=RKIND)                          :: dt             ! time diff
    !- ... vectors with trailing underscore
    real(kind=RKIND), dimension(3)            :: a_, v_         ! accel, velo
    
    a_ = (/-1, -2, -3/) !- Yes. This will convert the integers to the
                        ! (real) vector components
    v_ = 0              !- zeroing all components at once
    dt = 0.42           !- always good to know where the towel is...

    !> plain algebra
    ! \f[ \vec{v} \leftarrow \vec{v} + \Delta t \cdot 
    ! \left(\begin{array}{c} |a_1|\\ |a_2|\\ |a_3| \end{array}\right) \f]

    v_ = v_ + dt * abs(a_) !> this abs() works component-wise(!)

    write(*,*) v_   
end program vector_demo

Have fun!

Solkar