I am writeing a program which will contain many matrix manipulations.
I want to define my own operators to shorten the syntax for the matrix
manipulations. Below is a small program as example.

This program run fine using g95.

Using the ifort 9.1 compiler give error:
Syntax error, found '.' when expecting one of: ( , <END-OF-STATEMENT> ;
<IDENTIFIER> <CHAR_CON_KIND_PARAM> <CHAR_NAM_KIND_PARAM> ...
write(*,*) .t.(a.mm..ms.(Im+(.ms.btot).mm.s)) After commenting out this
line it runs fine.

The gfortran compiler warns:
matrixmantst.f90: In function vectorskew:
matrixmantst.f90:55: warning: Function does not return a value
matrixmantst.f90: In function matrixskew:
matrixmantst.f90:47: warning: Function does not return a value
and gives a segmentation fault when it is run.  If I changes:
  call skewmatrix(MatrixSkew,vec1(:,1))
by:
  real(dp) :: tmm(3,3)
  call skewmatrix(tmm,vec1(:,1))
  MatrixSkew = tmm
  (same for VectorSkew)
it runs fine without runtime checks, with runtime check it gives still
a segmentation fault

The Sun f95 compiler gives error:
public operator(.mm.),operator(.t.),operator(.ms.), skewmatrix
                               ^
"matrixmantst.f90", Line = 10, Column = 32: ERROR: A defined operator
must not be the same as a logical literal constant. After changing t by
tt it runs fine.

The PGI compiler gives:
PGF90-S-0034-Syntax error at or near ) (matrixmantst.f90: 102)
PGF90-S-0034-Syntax error at or near ) (matrixmantst.f90: 108)
By adding additional parentheses (.t.(a.mm.(.ms.(Im+(.ms.btot).mm.s))))
this error was is resolved and the program runs fine.

My questions are: Is this code according the F95 standards? Have you
any suggestions/comments how I can improve this code. Especially, how
can this be done so it will work for every F95 compiler?

Thanks in advance,

Johan

module types
! select kind
integer, parameter :: dp=kind(0.d0)
end module

module matrixman
! module for short matrix syntax
private

public operator(.mm.),operator(.t.),operator(.ms.), skewmatrix

interface operator (.mm.)
  module procedure MatrixMultiplication
end interface

interface operator (.t.)
  module procedure MatrixTranspose
end interface

interface operator (.ms.)
  module procedure MatrixSkew
  module procedure VectorSkew
end interface

contains
 function MatrixMultiplication(mat1,mat2)
  use types
  implicit none
  real(dp), intent(in) :: mat1(:,:), mat2(:,:)
  real(dp) :: MatrixMultiplication(size(mat1,dim=1),size(mat2,dim=2))
  MatrixMultiplication = matmul(mat1,mat2)
 end function

 function MatrixTranspose(mat1)
  use types
  implicit none
  real(dp), intent(in) :: mat1(:,:)
  real(dp) :: MatrixTranspose(size(mat1,dim=2),size(mat1,dim=1))
  MatrixTranspose = transpose(mat1)
 end function

 function MatrixSkew(vec1)
  use types
  implicit none
  real(dp), intent(in) :: vec1(3,1)
  real(dp) :: MatrixSkew(3,3)
  call skewmatrix(MatrixSkew,vec1(:,1))
 end function

 function VectorSkew(vec1)
  use types
  implicit none
  real(dp), intent(in) :: vec1(3)
  real(dp) :: VectorSkew(3,3)
  call skewmatrix(VectorSkew,vec1)
 end function

 subroutine skewmatrix(SMat,s)
  use types
  implicit none

  real(dp), intent(in) :: s(3)
  real(dp), intent(out) :: SMat(3,3)

  SMat(1,1) = 0.0_dp
  SMat(1,2) = -s(3)
  SMat(1,3) =  s(2)

  SMat(2,1) =  s(3)
  SMat(2,2) = 0.0_dp
  SMat(2,3) = -s(1)

  SMat(3,1) = -s(2)
  SMat(3,2) =  s(1)
  SMat(3,3) = 0.0_dp
 end subroutine
end module

program matrixtst
use types
use matrixman
implicit none
real(dp) :: res1(3,3), a(3,3), Im(3,3), btot(3,1), s(3,1)
real(dp) :: res2(3,3), bk(3,3), w1(3,1)

! filling the matrix with random numbers
call random_seed()
call random_number(a)
call random_number(Im)
call random_number(btot)
call random_number(s)

! original code
call skewmatrix(bk,btot)
bk = bk + Im
w1 = matmul(bk,s)
call skewmatrix(bk,w1)
res1 = transpose(matmul(a,bk))

! short code which should be equivalent
res2 =   .t.(a.mm..ms.(Im+(.ms.btot).mm.s))

write(*,*) res1
write(*,*)
write(*,*) res2
write(*,*)
write(*,*) .t.(a.mm..ms.(Im+(.ms.btot).mm.s))

This program runs fine using g95.

       Indeed.

Using the ifort 9.1 compiler give error:
Syntax error, found '.' when expecting one of: ( , <END-OF-STATEMENT> ;
<IDENTIFIER> <CHAR_CON_KIND_PARAM> <CHAR_NAM_KIND_PARAM> ...
write(*,*) .t.(a.mm..ms.(Im+(.ms.btot).mm.s)) After commenting out this
line it runs fine.

    The CVF compiler also doesn't like this but accepts the expression in
parentheses. The code is correct

The gfortran compiler warns:
matrixmantst.f90: In function 'vectorskew':
matrixmantst.f90:55: warning: Function does not return a value
matrixmantst.f90: In function 'matrixskew':
matrixmantst.f90:47: warning: Function does not return a value
and gives a segmentation fault when it is run.  If I changes:
  call skewmatrix(MatrixSkew,vec1(:,1))
by:
  real(dp) :: tmm(3,3)
  call skewmatrix(tmm,vec1(:,1))
  MatrixSkew = tmm
  (same for VectorSkew)
it runs fine without runtime checks, with runtime check it gives still
a segmentation fault

      gfortran is not checking properly. The code is correct.

The Sun f95 compiler gives error:
public operator(.mm.),operator(.t.),operator(.ms.), skewmatrix
                               ^
"matrixmantst.f90", Line = 10, Column = 32: ERROR: A defined operator
must not be the same as a logical literal constant. After changing t by
tt it runs fine.

     Some compilers accept .t. for .true. as an extension. As you may not
use .true. as an operator so, by extension, .t. becomes forbidden. A
compiler error, especially if running with standards checks on.

The PGI compiler gives:
PGF90-S-0034-Syntax error at or near ) (matrixmantst.f90: 102)
PGF90-S-0034-Syntax error at or near ) (matrixmantst.f90: 108)
By adding additional parentheses (.t.(a.mm.(.ms.(Im+(.ms.btot).mm.s))))
this error was is resolved and the program runs fine.

      See above.

Your code is correct, IMHO, and you have found some wonderful compiler bugs.

Regards,