DOUBLE COMPLEX variable returns NaN

[Feby_A_]

Hi!

I am using Intel Compiler 17.0 Update 2 with Visual Studio 2013 to compile a FORTRAN code. I am supposed to get a complex number after the compute process. However the real part of the variable returns an NaN.

To verify that there is no division by zero I did the same compute in the MATLAB environment, and it promptly returned the exepected complex number.

I have included a MWE for the same. Could someone throw light on what the issue is?

program complx1
    implicit none
    double complex :: dc
    dc = -(-(((1.00001489783669D0*1.1D0**2.0D0+&
(2.0D0*0.0D0*0.0D0+2.0D0*0.0D0*0.0D0)*1.1D0+1.00001374871743D0*0.0D0**2.0D0&
+2.0D0*0.0D0*0.0D0*0.0D0+1.00001374871743D0*0.0D0**2.0D0)*474615.661905876D0&
+3777440278.20392D0)*1.10002331748149D0**(5.0D0/3.0D0)&
-3777440278.20392D0*1.10002331748149D0**(2.0D0/3.0D0))*(-(1.0D0/2.0D0*3777440278.20392D0&
-1.0D0/2.0D0*162834746.546865D0/1.10002331748149D0)*8.43301084637337D0&
-1.0D0/2.0D0*474615.661905876D0*3.21004552381726D0)**((1.0D0&
-0.710000000000000D0)/0.710000000000000D0)*(1.0D0&
-0.710000000000000D0)/0.710000000000000D0*(1.0D0/2.0D0*3777440278.20392D0&
-1.0D0/2.0D0*162834746.546865D0/1.10002331748149D0)&
*0.999985102385248D0/(-(1.0D0/2.0D0*3777440278.20392D0&
-1.0D0/2.0D0*162834746.546865D0/1.10002331748149D0)*8.43301084637337D0&
-1.0D0/2.0D0*474615.661905876D0*3.21004552381726D0)&
+1.10002331748149D0**(5.0D0/3.0D0)*0.999985102385248D0*589000000000.000D0&
-1.0D0/3.0D0*1.10002331748149D0*5890000000.00000D0*((-1.0D0/3.0D0*3.21004552381726D0&
+1.00001489783669D0*1.1D0**2.0D0+(2.0D0*0.0D0*0.0D0+2.0D0*0.0D0*0.0D0)*1.1D0&
+1.00001374871743D0*0.0D0**2.0D0+2.0D0*0.0D0*0.0D0*0.0D0&
+1.00001374871743D0*0.0D0**2.0D0)*0.999985102385248D0+1.21000000000000D0&
-3.0D0*1.1D0**2.0D0))/1.10002331748149D0**(5.0D0/3.0D0)

    write (*,*) dc
    write (*,'(F0.0)') dc
    write (*,'(F0.0,A,F0.0)') dble(dc), ' + i ' , aimag(dc)
end program complx1

Here is a screengrab same computation performed on MATLAB.

[Arjen_Markus]

I got NaN with Intel Fortran 2018 as well, but when I tried to compile the program with gfortran I got the compile time error:

     1.10002331748149D0**(2.0D0/3.0D0))*(-(1.0D0/2.0D0*3777440278.20392D0-1.0D0/2.0D0*&
                                        1
Error: Raising a negative REAL at (1) to a REAL power is prohibited

Somewhere in this complex (no pun intended) expression you have a negative real that is raised to a real power. I think you should make that negative real a complex number for this to work.

[Feby_A_]

That was a life saver!

A DCMPLX type conversion worked out.

I guess Intel Compiler should throw up a warning for such cases.

Thank you Markus.

[Arjen_Markus]

I think the gfortran compiler uses a different strategy for these cases than the Intel Fortran compiler: the one uses compile-time evaluation, the other does not. I have not found a flag, though, that will cause the program to stop with an understandable error message, alas. May be the limited time I put into that. I did not try any of the IEEE routines to control floating-point behaviour - that mihgt be the way to go, as this is clearly an example of the calculations that are going on in your actual program.

[Steve_Lionel]

C:\Projects>ifort /fpe0 t.f90 /traceback
Intel(R) Visual Fortran Intel(R) 64 Compiler for applications running on Intel(R) 64, Version 19.0.2.190 Build 20190117
Copyright (C) 1985-2019 Intel Corporation.  All rights reserved.

Microsoft (R) Incremental Linker Version 14.15.26730.0
Copyright (C) Microsoft Corporation.  All rights reserved.

-out:t.exe
-subsystem:console
-incremental:no
t.obj

C:\Projects>t.exe
forrtl: error (65): floating invalid
Image              PC                Routine            Line        Source
t.exe              00007FF6076E3239  __libm_pow_e7               0  Unknown
t.exe              00007FF6076E1AB7  __libm_pow_dispat           0  Unknown
t.exe              00007FF60769105A  MAIN__                     10  t.f90

[Arjen_Markus]

I knew there was some option to get this result!  I just could not find it from the description from "ifort -help"

[Feby_A_]

Thank you Steve. I learned something new. Newbie here. :)