2
$\begingroup$

I need to use in Fortran, matrices that I create in Mathematica, therefore, I need to format them, so that Fortan can understand them. I focus on the simplest example:

Let's say I have tha matrix A created in Mathematica

A = {{1, 1}, {1, 1}};

Then, I am supposed to use FortranForm

FortranForm[A]

which gives as an output

List(List(1,1),List(1,1))

My question is, what do I do with this now? This cannot be the input file to Fortran, since this should be only numbers as far as I am aware. It could be that, the input file to Fortran is the out put of

List(List(1,1),List(1,1))

but this is nothing in Mathematica, so it does not give any output.

Any help please?

Improve this question
$\endgroup$
2
  • $\begingroup$ I think FortranForm was made for converting formulae to a form that's either usable with Fortran or is easy enough to edit to make it usable with Fortran. If it encounters a function it doesn't support, it keeps its name and uses parentheses for the call. In this case it thinks List is a function. $\endgroup$
    – Szabolcs
    Commented Jun 23, 2014 at 17:45
  • $\begingroup$ I had the same problem while converting an analytical matrix to fortran. It took me several regular expressions to get the output in a reasonable form. The biggest problem was the conversion of literal constants to double precision while list indices should remain integer... $\endgroup$
    – Stefan
    Commented Jun 24, 2014 at 5:17

1 Answer 1

Reset to default
5
$\begingroup$

FortranForm is really pretty limited. You need to do something like this:

 A = {{1, 1. 10^7}, {2., 1}}
 StringJoin@{"A=reshape((/", 
       Riffle[ ToString[FortranForm[#]] & /@ Flatten[A] , ","], 
          "/),shape(a))"}

"A=reshape((/1,1.e7,2.,1/),shape(a))"

or 

 StringJoin@{"data a/", 
     Riffle[ ToString[FortranForm[#]] & /@ Flatten[A] , ","], "/"}

"data a/1,1.e7,2.,1/"

( you likely want to Transpose[A] as well )

Improve this answer
$\endgroup$
6
  • $\begingroup$ Thanks alot for the answer, but, as far as I am aware, (and actually have checked) is that, if I want, Fortran to read my matrix A by using read* , the input file should be just a list of numbers with no comas, no brackets...and then Fortran will give them the position in the matrix according to the dimensions I set in the program $\endgroup$
    – Mencia
    Commented Jun 23, 2014 at 17:35
  • 1
    $\begingroup$ oh..for that just Export[filename,A,"Table"] and fortran will read it with a simple read(unit,*)a . (again you might want to Transpose[A] first.) $\endgroup$
    – george2079
    Commented Jun 23, 2014 at 17:42
  • $\begingroup$ You mean, read(unit,*), A ? $\endgroup$
    – Mencia
    Commented Jun 23, 2014 at 17:43
  • 1
    $\begingroup$ the extra comma is not needed. If you are reading from standard input you could use read*,a as well. $\endgroup$
    – george2079
    Commented Jun 23, 2014 at 17:47
  • $\begingroup$ @george2079 I am afraid you have made a mistake. Because fortran stores arrays as column major. for example {{1,2},{3,4}} in mathematica is actually reshape((/1,3,2,4/),(/2,2/)) in fortran. You have to transpose the list first $\endgroup$
    – matheorem
    Commented Dec 29, 2015 at 13:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.