fortran code problem

ztdep · September 6, 2009, 21:24

Dear firends:
I write a simple code with the fortran 95 , but i can not understantd the following.

I declare a double precdision number
Real*8 a=3.1
but when i out put it with
write(*,*) a
the Intel fortran give me the following
3.09999990463257
i can not understand this, could you please give me some hints.

Regards

Ananda Himansu · September 6, 2009, 22:28

Try
Real*8 a=3.1d0

ztdep · September 6, 2009, 23:28

thank you very much , it works.

3.1d0 means 3.1 is a double float number, but i have declare the variable a as real*8. then what is the difference
If i want 3.1 to be a long double float number, which symbol should i use.

Regards

Ananda Himansu · September 7, 2009, 10:22

You have to use the KIND parameter in the declaration of the variable. Also use a suffix of type real-kind for a constant such as 3.1. See any Fortran 90/95/2003 book or other documentation for the details. This will give you real*16 only if such a kind is available on the cpu architecture or if the compiler supports it through a library (the latter would be slow to execute). The actual value of the kind parameter depends on the architecture and compiler. You can use the PRECISION parameter to find the closest KIND.

ztdep · September 7, 2009, 10:40

Than you very much, Dear friends:
What is the difference between "Real*8 " and "Real(kind=8)", I think it is the same thing.

hadian · September 8, 2009, 04:22

real*8
real(8)
real(kind=8)
are the same

September 6, 2009, 21:24	fortran code problem	#1
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	Dear firends: I write a simple code with the fortran 95 , but i can not understantd the following. I declare a double precdision number Real8 a=3.1 but when i out put it with write(,*) a the Intel fortran give me the following 3.09999990463257 i can not understand this, could you please give me some hints. Regards

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September 6, 2009, 22:28		#2
Ananda Himansu New Member Ananda Himansu Join Date: Apr 2009 Location: Cleveland, Ohio, USA Posts: 17 Rep Power: 17	Try Real*8 a=3.1d0

September 6, 2009, 23:28		#3
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	thank you very much , it works. 3.1d0 means 3.1 is a double float number, but i have declare the variable a as real*8. then what is the difference If i want 3.1 to be a long double float number, which symbol should i use. Regards

September 7, 2009, 10:22		#4
Ananda Himansu New Member Ananda Himansu Join Date: Apr 2009 Location: Cleveland, Ohio, USA Posts: 17 Rep Power: 17	You have to use the KIND parameter in the declaration of the variable. Also use a suffix of type real-kind for a constant such as 3.1. See any Fortran 90/95/2003 book or other documentation for the details. This will give you real*16 only if such a kind is available on the cpu architecture or if the compiler supports it through a library (the latter would be slow to execute). The actual value of the kind parameter depends on the architecture and compiler. You can use the PRECISION parameter to find the closest KIND.

September 7, 2009, 10:40		#5
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	Than you very much, Dear friends: What is the difference between "Real*8 " and "Real(kind=8)", I think it is the same thing.

September 8, 2009, 04:22		#6
hadian Member Mohammad Reza Hadian Join Date: Mar 2009 Location: Yazd, Iran Posts: 52 Rep Power: 17	real*8 real(8) real(kind=8) are the same