CODEWITHSUNDEEP
fortranprecisiongfortranfortran95silverfrost-fortran
ZeroTwo
ZeroTwo

Reputation: 317

Double precision in Fortran for trignometric functions

I am using the following code to calculate cos for pi/2 in Fortran.

program precision_Fortran
  IMPLICIT  NONE
  !!integer, parameter :: dp = kind(1.0d0) !!Gives same result as line below
  integer, parameter :: dp = selected_real_kind(15, 307)
  
  Real(dp), parameter:: pi=4.0*atan(1.0)
  Real(dp) :: angle

  angle = cos(pi/2.0)
  
  write(*,*)'pi = ', pi
  write(*,*)'angle = ', angle
     
end program precision_Fortran

I compiled using gfortran and ftn95. From both, the output is

 pi =    3.1415927410125732
 angle =   -4.3711390001862412E-008

How do I get a better precision for angle here? For instance in C++ I see it in order of E-18, for all declaration using double.

Please let me know if more information is needed to explain it better.

Extra : The main code I am using, with physical equations having trigonometric terms, is having precision issues, and am not entirely sure, but am suspecting it's because of this. So, want to check if above could be improved somehow. Not expert with Fortran so struggling to figure this out.

Upvotes: 1

Views: 561

Answers (0)

Related Questions