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Fortran: help with arguments to a pre-built software

  1. Apr 27, 2012 #1
    There are two functions that I need help with:

    http://www.maths.uq.edu.au/expokit/fortran/dgpadm.f
    http://www.maths.uq.edu.au/expokit/fortran/dgchbv.f

    The problem I'm having is that the arguments on the line DGPADM(....) don't match identically with the explanation. For example, H, ldh and m vs. m and H(ldh,m) not sure why there is a parenthesis. If someone could give me a simple example of acceptable parameters that I could try out,that would be greatly appreciated.

    I understand what to put for ideg, m, t, but not so sure about wsp, ipiv , H or the others. For example, H is a matrix, so I guess it needs a matrix as an argument..... regardless could someone help me out here?! Thanks!

    In the first case:
    subroutine DGPADM( ideg,m,t,H,ldh,wsp,lwsp,ipiv,iexph,ns,iflag )

    * ideg : (input) the degre of the diagonal Pade to be used.
    * a value of 6 is generally satisfactory.
    *
    * m : (input) order of H.
    *
    * H(ldh,m) : (input) argument matrix.
    *
    * t : (input) time-scale (can be < 0).
    *
    * wsp(lwsp) : (workspace/output) lwsp .ge. 4*m*m+ideg+1.
    *
    * ipiv(m) : (workspace)
    *
    *>>>> iexph : (output) number such that wsp(iexph) points to exp(tH)
    * i.e., exp(tH) is located at wsp(iexph ... iexph+m*m-1)
    * ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    * NOTE: if the routine was called with wsp(iptr),
    * then exp(tH) will start at wsp(iptr+iexph-1).
    *
    * ns : (output) number of scaling-squaring used.
    *
    * iflag : (output) exit flag.
    * 0 - no problem
    * <0 - problem


    Second case:
    subroutine DGCHBV( m, t, H,ldh, y, wsp, iwsp, iflag )

    * m : (input) order of the matrix H
    *
    * t : (input) time-scaling factor (can be < 0).
    *
    * H(ldh,m): (input) argument matrix.
    *
    * y(m) : (input/output) on input the operand vector,
    * on output the resulting vector exp(t*H)*y.
    *
    * iwsp(m) : (workspace)
    *
    * wsp : (workspace). Observe that a double precision vector of
    * length 2*m*(m+2) can be used as well when calling this
    * routine (thus avoiding an idle complex array elsewhere)
     
  2. jcsd
  3. Apr 27, 2012 #2

    Mark44

    Staff: Mentor

    Mod note: moved to Prog & CS section
     
  4. Apr 27, 2012 #3

    Mark44

    Staff: Mentor

    I'll take a stab at the first one.

    H - the name of a two-dimensional matrix - the matrix contains double precision numbers.
    ldh - # of rows in matrix H - an integer.
    m - # of cols in matrix H - an integer.
    t - timescale. This is the constant t in etH -- double precision.
    wsp - workspace - an output array with lwsp elements, each of type double precision.
    lwsp - # of elements of the wsp array - an integer. It needs to be > 4m2 + ideg + 1.
    ipiv - an output array with m integer elements.
    iexph - an index into the wsp array - an integer.
    The computed elements of etH are located in the wsp array. They start at wsp(iexph) and end at wsp(iexph + m2 - 1). This section of the array contains all of the elements of etH.
    ns - no clue - integer.
    iflag - a flag that indicates whether the calculation was successful or not. Negative value indicates some kind of error.

    I would start with a very simple matrix, like
    $$H = \begin{bmatrix} 0 & 1 \\ 0 & 0 \end{bmatrix}$$
    and a value of 1.0 for t.

    You should end up with
    $$e^{tH} = \begin{bmatrix} 1 & 1 \\ 0 & 1 \end{bmatrix}$$

    The variables that are identified as being output don't need to be initialized before calling this routine. The other variables need to be initialized before the call.

     
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