如何在 Fortran 中以固定格式打印极小的双精度数? [英] How do I print extremely small double precision numbers with fixed format in Fortran?

问题描述

有没有办法在 Fortran 中以固定格式打印极小的双精度数字?不知何故，E"被截断了.

Is there a way to print extremely small double precision numbers with fixed format in Fortran? Somehow, the "E" gets truncated.

在下面的代码中将ES15"更改为ES18"没有帮助:

Changing the 'ES15' to 'ES18' in the code below doesn't help:

program print_double
  implicit none
  double precision :: x
  x = 2.71818D-200
  write(*,*)                 "fmt=*     : x = ", x
  write(*,fmt='(A,ES15.3)') " fmt=ES15.3: x = ", x
  write(*,fmt='(A,E15.3)')  " fmt= E15.3: x = ", x
end program print_double

这是输出:

$ gfortran print_double.f90 -o print_double && ./print_double
 fmt=*     : x =    2.7181800000000000E-200
 fmt=ES15.3: x =       2.718-200
 fmt= E15.3: x =       0.272-199

$ ifort print_double.f90 -o print_double && ./print_double
 fmt=*     : x =   2.718180000000000E-200
 fmt=ES15.3: x =       2.718-200
 fmt= E15.3: x =       0.272-199

注意:这是用于检查通过两种不同数学方法获得的解决方案是否一致的代码.大多数情况下，差异很小(即远低于机器精度)，但情况可能并非总是如此.

Note: this is for a code in which I check that the solution obtained through two different mathematical approaches agree. Most of the the time, the differences are small (i.e. well below machine precision), but this may not always be the case.

推荐答案

您可以使用 Ew.dEe 描述符指定指数中的位数.它也适用于科学和工程格式.

You can specify the number of digits in the exponent using the Ew.dEe descriptor. It also works for Scientific and Engineering formats.

write(*,fmt='(A,ES15.3E3)') " fmt=ES15.3E3: x = ", x

给予

fmt=ES15.3E3: x = 2.718E-200

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