Parameter Value returns wrong Answer using Floor()

[richard_griffin]

If you create a Numeric parameter (mm) and type in 1348.5 and run the code below, the message box returns 3.

test = Floor((Test - 322 - 90.5 - 136) / 200)

MessageBox.Show(test, "Msg")

 If you remove Test from the code and type in 1348.5

test = Floor((1348.5 - 322 - 90.5 - 136) / 200)

MessageBox.Show(test, "Msg")

It returns 4 which is correct.

Can someone explain why this is the case and if possible, a way to get the parameter version to return the correct answer?

[clutsa]

There are some known issues in converting from Inventor to iLogic...

https://forums.autodesk.com/t5/inventor-customization/attack-of-the-doubleforequals/m-p/5808334

My math says 3 would be right though.  (790)/200=3.95 the floor of which is 3.

Edit: I managed to misstype 322 as 332 in several different places... now I see what you're saying. 

[richard_griffin]

Edit: I saw your edit when it was too late. 

Its just when it takes the value from the parameter that it goes wrong which is really confusing.

Using a parameter with 1148.5 returns the correct answer (600 / 200).

Its like one rogue parameter that isnt converting correctly.

[clutsa]

Can you use...

test = Floor((Round(Test,8) - 322 - 90.5 - 136) / 200)

 it seems to help on mine but I'm using inches so I have extra math to convert mine to metric and I may just be correcting that rounding error. 

[richard_griffin]

Yeah that does work, I tried that a little while ago.

It doesn't change the fact that its using the incorrect number for the parameter though which is concerning.

[clutsa]

Also this seems to work...

test = Floor(((Parameter.Param("Test").Value*10) - 322 - 90.5 - 136) / 200)

but I know that's not helpful because it's basically the same kind of workaround...

I think @MjDeck got it right in post 11 of the link I posted earlier. 

[clutsa]

Sorry, I meant to @xiaodong_liang in the last post to get his thoughts too.

[MjDeck]

@richard_griffin , I agree with @clutsa's suggesstion to use Round.
The parameter value in the rule is slightly incorrect because of rounding error when converting units. But it is very, very close. You can see that by running this code:

MessageBox.Show("Test - 1348.5 = " & Test - 1348.5)

You can also see the problem in the Parameters dialog. Create a new parameter named Test_ul with units of ul. Enter this Equation for it:

isolate(Test;mm;ul) - 1348.5 ul

The isolate function converts the value to ul.
You'll see that the value shown for that parameter is -0.00000. It's very close to zero, but it's negative.

[richard_griffin]

Thanks for your response, our in house Developer has had a look at it and it and he says its a bit more than a conversion issue, he created a rule to explicitly handle the mm conversion to ensure we have the correct value from the start. 

Is this something worth opening a case over? I can send you his code if you'd like to take a look.

[bradeneuropeArthur]

I have seen that floor better (only) work with unitless parameters!

This means that you need to convert the parameters first to "ul" than floor or Ceil this "ul" parameter.

Than after Ceil of Floor, convert it back to mm or equal as you prefer.

Regards,

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[richard_griffin]

It appears the issue isnt with Floor() itself, but rather with the way Inventor is using the Parameter. Its 'close to' the actual value, but not the value which in turn causes floor to return the wrong answer.

[clutsa]

@richard_griffin I'm never going to say "No, I don't want to see some code." If you post it and I find it worthless I didn't waste much time looking at it but if it's something I've never thought of I can learn something new. That's why I help on the forum is to learn myself and help teach others along the way. I've learned more about how Inventor/iLogic work trying to figure out how to solve someone else's problems then I ever would have just trying to solve my own. 

So long story short, yes, please share the code... even if none of the people in the current conversation need it someone else down the road may learn from it. 

[MjDeck]

@richard_griffin , please share the code. If it's more than a conversion issue then we should open a case for it.

[MjDeck · Accepted solution]

Here's a demonstration of roundoff error in converting units. Parameter values are stored internally in units of cm.
Open a web browser, and hit F12 to bring up the Developer Tools.
Click on the Console tab.
Enter these commands:

let x = 1348.5
let x_cm = x / 10
let x_mm = x_cm / 0.1
x_mm - 1348.5

The output should be:
-2.2737367544323206e-13

[richard_griffin]

I have opened a ticket, if you have access to it and would like to take a look. 15031339

[MjDeck · Accepted solution]

I looked at the code you provided in the ticket. To see that the problem is caused by roundoff in the units conversion:
After this line:

Dim mmValue As Double = oUnitsOfMeasure.ConvertUnits(inventorValue.ModelValue, Inventor.UnitsTypeEnum.kCentimeterLengthUnits, Inventor.UnitsTypeEnum.kMillimeterLengthUnits) 

Add this line:

Trace.WriteLine("mmValue - 1348.5 = {0}", mmValue - 1348.5)

[MjDeck · Accepted solution]

@richard_griffin , we have improved the accuracy of the units conversion in the Inventor 2020.2 Update. (Internal issue number INVGEN-12769.)
In 2020.2, no workaround is needed. Your original code will give the expected answer.