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how to to include following formula in the FortranForm in a correct format?

R = 
  Compile[{{y}}, 
    Piecewise[{{1.31446 Tan[1.58986 y] + 0.91209 y, 
       Abs[y] < 0.84136}, {1./(Sign[y] - y), 
       0.841360 <= Abs[y] < 1.}}], 
    RuntimeOptions -> "EvaluateSymbolically" -> False 
    , Parallelization -> True, 
    CompilationTarget -> "C"] //FullSimplify;
 DR=D[R[a],a];
FortranForm[DR]
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  • 1
    $\begingroup$ I don't know of any code to create Fortran from WL compiled code, but perhaps you could use CCodeGenerate instead to create C code? $\endgroup$
    – Carl Woll
    Commented Dec 28, 2017 at 17:18
  • $\begingroup$ @CarlWoll how about uncompiled version of the code... unfortunately the code is in fortran :) $\endgroup$
    – user49047
    Commented Dec 28, 2017 at 17:34
  • $\begingroup$ Applying D to your function R is meaningless. If you want to see the C-code for R, use ExportString[R,"C"]. You have to search a bit for the relevant part of the code, though. Afterwards, you can easily translate it to fortran by hand (at least the standard arithmetics can be copied)... $\endgroup$
    – Henrik Schumacher
    Commented Dec 28, 2017 at 17:38
  • 1
    $\begingroup$ Can’t you call a C function from Fortran? $\endgroup$
    – Carl Woll
    Commented Dec 28, 2017 at 17:39
  • $\begingroup$ can you explain better what you are actually trying to do? I cant see any reason to use Compile at all if the goal is to create fortran code. $\endgroup$
    – george2079
    Commented Dec 28, 2017 at 19:52

1 Answer 1

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this is simple enough to do by hand..you will spend more time trying to automate the process than just typing the code out.

First a little manipulation of the original expression to get rid of the Abs

cons = {
  c1 -> 1.31446,
  c2 -> 1.58986,
  c3 -> 0.91209,
  c4 -> 0.84136}
dp = Piecewise[
  {{c1 Tan[c2 y] + c3 y, Abs[y] < c4},
   {1/(1 - y), c4 <= y < 1},
   {-1/(1 + y), -1 < y <= -c4 }}]
dd = D[dp, y]

enter image description here

here you can use FortranForm to pull out parts of the expression:

  FortranForm[dd[[1, 1, 1]]]

c3 + c1*c2*Sec(c2*y)**2

just do that as needed and paste to the code as you write:

    real function df(y)
    implicit none
    real::y
    real,parameter::c1=1.31446,c2=1.58986,c3=0.91209,c4=0.84136
    if(abs(y).gt.1)then
      df=0
    elseif( y.le.-c4)then
      df=(1+y)**(-2)
    elseif(y.gt.c4)then
      df=(1-y)**2
    else
      df=c3 + c1*c2*Sec(c2*y)**2
    endif
   end
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  • $\begingroup$ @geogerge2079, how can we define real*8 value: e.g. 1.d0, 2.d0 etc??? it could be useful in fortran coding $\endgroup$
    – ABCDEMMM
    Commented Oct 29, 2018 at 1:26

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