Hello Everyone,

Looks like I'm stumped again.  I have a simple polynomial calculation (7th order) where the result in SCL is "NaN".  Not sure why, I'm not doing any root or logs that might make the calculation sensitive to negative numbers or certain values.

Don't have idea why NaN.

But a little hint - use Horner's method for calculating poly value.

jacek d

Don't have idea why NaN.

But a little hint - use Horner's method for calculating poly value.

result out of allowed numeric area / divison by Zero (?)

Nate@SMS

 I have a simple polynomial calculation (7th order) where the result in SCL is "NaN".
...

Hi there.

I am very curious about this case..
so I went ahead and coded (copy-paste) for an S7-1200.
The simulation result is not what you got.
The code and picture of the simulation result is attached.

What result did you expect?

Sorry - TIA Portal is what I have available.
What is the calculation for?

Maybe someone wants to build on the code run on an S7-300 / S7-400?

Greetings.
w

FUNCTION "CALC" : Void
{ S7_Optimized_Access := 'TRUE' }
VERSION : 0.1
VAR_INPUT
Exc1Angle : Real;
END_VAR

VAR_OUTPUT
OUT : Real;
END_VAR

VAR_TEMP
Form2Acoeff : Real;
Form2Bcoeff : Real;
Form2Ccoeff : Real;
Form3Acoeff : Real;
Form3Bcoeff : Real;
Form3Ccoeff : Real;
Form3Dcoeff : Real;
Form3Ecoeff : Real;
Form3Fcoeff : Real;
Form3Gcoeff : Real;
Form4Acoeff : Real;
Form4Bcoeff : Real;
Form4Ccoeff : Real;
GapActTemp : Real;
END_VAR

BEGIN
//Initialize all the temporary parameters
#Form2Acoeff := 0.000076; //2nd degree term coefficient
#Form2Bcoeff := 0.000557; //1st degree term coefficient
#Form2Ccoeff := -0.004;    //Constant
#Form3Acoeff := 8317.0;   //6th degree term coefficient
#Form3Bcoeff := -9035.0;   //5th degree term coefficient
#Form3Ccoeff := 3936.3;   //4th degree term coefficient
#Form3Dcoeff := -887.3;    //3rd degree term coefficient
#Form3Ecoeff := 115.24;   //2nd degree term coefficient
#Form3Fcoeff := -10.92;    //1st degree term coefficient
#Form3Gcoeff := -0.0345;   //Constant
#Form4Acoeff := -0.00044;  //2nd degree term coefficient
#Form4Bcoeff := 0.0395;   //1st degree term coefficient
#Form4Ccoeff := 0.0;      //Constant

#GapActTemp := #Form2Acoeff * #Exc1Angle ** 2
+ #Form2Bcoeff * #Exc1Angle + #Form2Ccoeff;

#OUT := #Form3Acoeff * #GapActTemp ** 6
+ #Form3Bcoeff * #GapActTemp ** 5
+ #Form3Ccoeff * #GapActTemp ** 4
+ #Form3Dcoeff * #GapActTemp ** 3
+ #Form3Ecoeff * #GapActTemp ** 2
+ #Form3Fcoeff * #GapActTemp
+ #Form3Gcoeff;

END_FUNCTION

Marko Bursic

The correct use of multipier in SCL is * and not **. 

 ** is an exponentiation.

Hello Everyone,

Thanks for all the feedback.  I read some material and tried some more things and here's where I'm at today:

From a standpoint of optimal computational accuracy, you are all right, there are much better ways to do this.  Probably the most accurate method is to solve for the roots of the polynomial and factor it, that way the numbers are not so radically different when the math is computed.  Problem is this polynomial has 5 imaginary roots and would be really messy to pull out the only 2 real ones, although it'd help a bit from a standpoint of accuracy.  HOWEVER, my problem has nothing to do with accuracy.  S7 doesn't throw NaN or any other errors if you're doing doing the most optimal calculation, it'll just round.  So that's not my issue.

My issue is much stranger.  Turns out in SCL,  I cannot take the power of a negative number greater than 2!!!  This seems like some sort of mistake with the hardware/software, and at this point I need to look at the STL generated block to understand the problem, but take this much more simple example.

This code here works fine for the smallest REAL, positive value that S7 can represent: 

Nate@SMS

This code here works fine for the smallest REAL, positive value that S7 can represent: 

GapAct:= +1.0e-32;

Exc1OverlapAct:= 8317.0*(GapAct**6)

- 9035.0*(GapAct**5)

+ 3936.3*(GapAct**4)

- 887.3*(GapAct**3)

+ 115.24*(GapAct**2)

- 10.92*(GapAct)

- 0.0345;

 Also, if GapAct = 0.0 it works fine as well, but any negative value, ranging from -1.0e-32 to -9.9e+32, returns NaN.

Furthermore, this simple logic:

TempA:= -1.0;

TempB:= TempA**3;

Returns a value of '-1.#IND00e+000' for TempB.   I don't understand this value.

 I've checked William's code generated for S7-300 on a simulator. Works fine.

Where have you found the limits for REALs? That's the correct values:

-3.402823e+38 to -1.175495e-38

±0.0

+1.175495e-38 to +3.402823e+38

The code for -1**3 also is ok while simulated, i.e. the result is -1.0 as expected.

Could you post whole SCL code (i.e. including vars declaration) ?

As a S7 has only an EXP (base e) function and not Power, your formula is internally transferred into:

L     -1.000000e+000
T     #TempA
L     #TempA
LN
L     3.000000e+000
*R
EXP
T     #TempB

Thus, if TempA is negative, then LN will fail.

Change all power calculations to the number of multiplication (or use a new function which calculates the power):

TempA:= -1.0;
TempB:= (TempA * TempA * TempA);