blocks|key|17305|text|不是的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|17306|用于生成/检查NaN的IEEE_ARITHMETIC的突出部分非常容易为特定体系结构的gfortran编写。|17307|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

No.

The salient parts of IEEE_ARITHMETIC for generating/checking for NaN's are easy enough to write for gfortran for a particular architecture.

blocks|key|2415275|text|不使用ieee_arithmatic的简单方法是执行以下操作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2415276|Infinity：定义变量infinity+=+HUGE(dbl_prec_var)+(如果有，则定义四精度变量)。然后，您可以通过if(my_var+>+infinity)简单地检查变量是否为无穷大。|BOLD|2415277|NAN：这就更容易了。按照定义，NAN并不等于任何东西，甚至其本身。简单地将变量与其自身进行比较：if(my_var+/=+my_var)。|2415278|entityMap^0|3|F|0|0|8|D|T|1U|L|0|0|3|1D|K|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|P|8|@$9|Q|A|R|B|H]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|I|3|J|5|6|7|W|8|@$9|X|A|Y|B|H]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|K|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|L|$]]

The simple way without using the <code>ieee_arithmatic</code> is to do the following.

Infinity: Define your variable <code>infinity = HUGE(dbl_prec_var)</code> (or, if you have it, a quad precision variable). Then you can simply check to see if your variable is infinity by <code>if(my_var &gt; infinity)</code>.

NAN: This is even easier. By definition, NAN is not equal to anything, even itself. Simply compare the variable to itself: <code>if(my_var /= my_var)</code>.

blocks|key|2415289|text|不是的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2415290|在Fortran+90/95中，也没有一种符合标准的方法来检查无穷大或NaNs，也没有符合标准的方法。在Fortran+90/95中，没有一种符合标准的方法来定义这些准数字。|2415291|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

No.

Neither is there a standards-compliant way of checking for infinities or NaNs in Fortran 90/95, nor can there be a standards-compliant way. There is no standards-compliant way of defining either of these quasi-numbers in Fortran 90/95.

blocks|key|2415299|text|对于Inf来说，如果(A-1+.eq+).(+A)为真，则A为Inf。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2415300|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

For Inf it seems to work that if (A-1 .eq. A) is true, then A is Inf

blocks|key|2415302|text|我没有足够的代表来评论，所以我会“回答”里克汤普森关于测试无穷大的建议。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2415303|if+(A-1+.eq.+A)+|code-block|syntax|javascript|2415304|如果A是一个很大的浮点数，并且1低于A的精度，这也是正确的。|offset|length|style|CODE|2415305|一个简单的测试：|2415306|subroutine+test_inf_1(A)
++++real,+intent(in)+::+A
++++print*,+"Test+(A-1+==+A)"
++++if+(A-1+.eq.+A)+then
++++++++print*,+"++++INFINITY!!!"
++++else
++++++++print*,+"++++NOT+infinite"
++++endif
end+subroutine

subroutine+test_inf_2(A)
++++real,+intent(in)+::+A
++++print*,+"Test+(A+>+HUGE(A))"
++++if+(A+>+HUGE(A))+then
++++++++print*,+"++++INFINITY!!!"
++++else
++++++++print*,+"++++NOT+infinite"
++++endif
end+subroutine


program+test
++++real+::+A,B

++++A=10
++++print*,+"A+=+",A
++++call+test_inf_1(A)
++++call+test_inf_2(A)
++++print*,+""

++++A=1e20
++++print*,+"A+=+",A
++++call+test_inf_1(A)
++++call+test_inf_2(A)
++++print*,+""

++++B=0.0+!+B+is+necessary+to+trick+gfortran+into+compiling+this
++++A=1/B
++++print*,+"A+=+",A
++++call+test_inf_1(A)
++++call+test_inf_2(A)
++++print*,+""

end+program+test|2415307|产出：|2415308|A+=++++10.0000000++++
Test+(A-1+==+A)
++++NOT+infinite
Test+(A+>+HUGE(A))
++++NOT+infinite

A+=++++1.00000002E%2B20
Test+(A-1+==+A)
++++INFINITY!!!
Test+(A+>+HUGE(A))
++++NOT+infinite

A+=++++++++++Infinity
Test+(A-1+==+A)
++++INFINITY!!!
Test+(A+>+HUGE(A))
++++INFINITY!!!|2415309|entityMap^0|0|0|F|1|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@$I|Z|J|10|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

I don't have enough rep to comment so I'll "answer" regarding Rick Thompson's suggestion for testing infinity. 

<pre><code>if (A-1 .eq. A) 
</code></pre>

This will also be true if A is a very large floating point number, and <code>1</code> is below the precision of A. 

A simple test: 

<pre><code>subroutine test_inf_1(A)
 real, intent(in) :: A
 print*, "Test (A-1 == A)"
 if (A-1 .eq. A) then
 print*, " INFINITY!!!"
 else
 print*, " NOT infinite"
 endif
end subroutine

subroutine test_inf_2(A)
 real, intent(in) :: A
 print*, "Test (A &gt; HUGE(A))"
 if (A &gt; HUGE(A)) then
 print*, " INFINITY!!!"
 else
 print*, " NOT infinite"
 endif
end subroutine


program test
 real :: A,B

 A=10
 print*, "A = ",A
 call test_inf_1(A)
 call test_inf_2(A)
 print*, ""

 A=1e20
 print*, "A = ",A
 call test_inf_1(A)
 call test_inf_2(A)
 print*, ""

 B=0.0 ! B is necessary to trick gfortran into compiling this
 A=1/B
 print*, "A = ",A
 call test_inf_1(A)
 call test_inf_2(A)
 print*, ""

end program test
</code></pre>

outputs: 

<pre><code>A = 10.0000000 
Test (A-1 == A)
 NOT infinite
Test (A &gt; HUGE(A))
 NOT infinite

A = 1.00000002E+20
Test (A-1 == A)
 INFINITY!!!
Test (A &gt; HUGE(A))
 NOT infinite

A = Infinity
Test (A-1 == A)
 INFINITY!!!
Test (A &gt; HUGE(A))
 INFINITY!!!
</code></pre>

blocks|key|17378|text|我用过：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|17379|++PROGRAM+MYTEST
++USE,+INTRINSIC+::+IEEE_ARITHMETIC,+ONLY:+IEEE_IS_FINITE++++++
++DOUBLE+PRECISION+::+number,+test
++number+=+'the+expression+to+test'
++test+=+number/number
++IF+(IEEE_IS_FINITE(test))+THEN
+++++WRITE(*,*)+'We+are+OK'
++ELSE
+++++WRITE(*,*)+'Got+a+problem'
++END+IF+++++++++
+++++WRITE(*,*)+number,+test
++END+PROGRAM+MYTEST|code-block|syntax|javascript|17380|这将打印出数字=+0.0D0、1.0D0/0.0D0、0.0D0/0.0D0、SQRT(-2.0D0)的“Got+a+problem”，以及对于诸如number+=EXP(1.0D+800)或number+=+EXP(-1.0D800)的溢出和欠流量。注意，通常情况下，诸如number+=+EXP(1.0D-800)将只设置number+=+1.0，并在编译时生成警告，但是程序会打印‘我们很好’，我认为这是可以接受的。|17381|奥尔。|17382|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I have used:

<pre><code> PROGRAM MYTEST
 USE, INTRINSIC :: IEEE_ARITHMETIC, ONLY: IEEE_IS_FINITE 
 DOUBLE PRECISION :: number, test
 number = 'the expression to test'
 test = number/number
 IF (IEEE_IS_FINITE(test)) THEN
 WRITE(*,*) 'We are OK'
 ELSE
 WRITE(*,*) 'Got a problem'
 END IF 
 WRITE(*,*) number, test
 END PROGRAM MYTEST
</code></pre>

This will print 'Got a problem' for number = 0.0D0, 1.0D0/0.0D0, 0.0D0/0.0D0, SQRT(-2.0D0), and also for overflows and underflows such as number = EXP(1.0D800) or number = EXP(-1.0D800). Notice that generally, things like number = EXP(1.0D-800) will just set number = 1.0 and produce a warning at compilation time, but the program will print 'We are OK', which I find acceptable.

OL.

blocks|key|17392|text|因此，对于Fortran，1/无穷大=0，将变量除以零即|type|unstyled|depth|inlineStyleRanges|entityRanges|data|17393|program+test
implicit+none
real+::+res
integer+::+i

do+i=1,1000000
++++res=-log((1.%2B(10**(-real(i))))-1.)
++++print*,i,res
++++if+((1./res)==0.)+then
++++++++exit
++++end+if
end+do

end+program|code-block|syntax|javascript|17394|这是你的无穷大支票。没有必要出现并发症。|17395|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For Fortran, 1/infinity=0
thus, divide your variable by zero
i.e 

<pre><code>program test
implicit none
real :: res
integer :: i

do i=1,1000000
 res=-log((1.+(10**(-real(i))))-1.)
 print*,i,res
 if ((1./res)==0.) then
 exit
 end if
end do

end program
</code></pre>

there's your infinity check. No complication necessary.

blocks|key|1095540|text|对于测试NaN，没有一件事情是有效的，eg.if测试了真正的s2p，看看它是否是NaN。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1095541|if(isnan(s2p))+|code-block|syntax|javascript|1095542|没有在gfortran工作，也没有|1095543|if(s2p.ne.s2p).+|1095544|唯一起作用的是|1095545|if(.not.s2p<1.and..not.s2p>1)++|1095546|不过，为了确保您可以添加|1095547|if(.not.s2p<1.and..not.s2p>1.and..not.s2p==1)++++|1095548|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

for testing NaN none of the things worked eg.if testing real s2p to see if it is NaN then
<pre><code>if(isnan(s2p)) 
</code></pre>
did not work in gfortran nor did
<pre><code>if(s2p.ne.s2p). 
</code></pre>
The only thing that worked was
<pre><code>if(.not.s2p&lt;1.and..not.s2p&gt;1) 
</code></pre>
though to make real sure u may want to add
<pre><code>if(.not.s2p&lt;1.and..not.s2p&gt;1.and..not.s2p==1) 
</code></pre>

I've been trying to find a standards-compliant way to check for Infinite and NaN values in Fortran 90/95 but it proved harder than I thought.

<ul>
<li>I tried to manually create Inf and NaN variables using the binary representation described in IEEE 754, but I found no such functionality.</li>
<li>I am aware of the intrinsic <code>ieee_arithmetic</code> module in Fortran 2003 with the <code>ieee_is_nan()</code> and <code>ieee_is_finite()</code> intrinsic functions. However it's not supported by all the compilers (<a href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29383" rel="noreferrer">notably gfortran</a> as of version 4.9).</li>
</ul>

Defining infinity and NaN at the beginning like <code>pinf = 1. / 0</code> and <code>nan = 0. / 0</code> seems hackish to me and IMHO can raise some building problems - for example if some compilers check this in compile time one would have to provide a special flag.

Is there a way I can implement in standard Fortran 90/95?

<pre><code>function isinf(x)
! Returns .true. if x is infinity, .false. otherwise
...
end function isinf
</code></pre>

and <code>isnan()</code>?

Is there a standard way to check for Infinite and NaN in Fortran 90/95?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我一直试图找到一种符合标准的方法来检查Fortran 90/95中的无限值和NaN值，但事实证明这比我想象的要困难。我尝试使用IEEE754中描述的二进制表示来手动创建Inf和NaN变量，但是我没有发现这样的功能。我知道Fortran 2003中带有ieee_is_nan()和ieee_is_finite()内在函数的...

问在Fortran 90/95中是否有检查无限和NaN的标准方法？
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问在Fortran 90/95中是否有检查无限和NaN的标准方法？EN