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A
Alvaro_951-Visitor
1-Visitor
October 12, 2019
Solved

Prime 6.0 - Ceil and Floor function error

  • October 12, 2019
  • 5 replies
  • 8771 views

Hello everyone,

 

I am experiencing the same rounding error from previous versions in Mathcad Prime 6.0. Have an explanation?  Or, where can I report effectively this error?

 

Thanks!

 

clipboard_image_0.png

Best answer by Werner_E

The solution is simple.

Check "Approximate Equality" ("Calculation" ribbon, "Calculation Options") and you should get the correct result:

clipboard_image_0.png

clipboard_image_0.png

5 replies

W
Werner_E25-Diamond I
25-Diamond I
October 13, 2019
@Alvaro_95 wrote:

Hello everyone,

 

I am experiencing the same rounding error from previous versions in Mathcad Prime 6.0. Have an explanation?  Or, where can I report effectively this error?

Effectively? Nowhere! Don't forget - we are dealing with PTC and they have proven their ... "efficiency" in program development and bug fixing quite effective if you look at the way they "develop" Prime.

If you really go through the hassle of reporting this effect you can open a support case, but only if you have paid them and are under maintenance. The lack of a channel in which everybody can report bugs already tells the whole story about PTCs interest in making their software more bug-free.

 

BTW, AFAIR this bug has already been reported here in the forum a few times (its also present in real Mathcad, so its rather old)  and also shows up without using units:

clipboard_image_0.png

 

 

A
Alvaro_951-VisitorAuthor
1-Visitor
October 13, 2019
Thank you Werner. I will try to report via support contact.
And yes, it will be useful to have a label "report" just as "tips" or "ideas" in the community.
W
Werner_E25-Diamond I
25-Diamond I
October 13, 2019
@Alvaro_95 wrote:
Thank you Werner. I will try to report via support contact.
And yes, it will be useful to have a label "report" just as "tips" or "ideas" in the community.

This label would only make sense, if relevant PTC-staff would scan a subforum like this on a regular basis and act accordingly. I guess this never will happen. Good luck with your support case.

 

BTW, in MC15 we can set the number of decimal places to 17 and that way we can see whats happening. This at least partially explains the effect - internal round-off errors - possibly due to conversion from decimal in IEEE binary format. The effect also shows if we set the result to 15 decimal numbers. If we do that in Prime (15 is the max possible here), we are not shown that round-off error but obviously its there as we still have the bug in "floor" etc.

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T
21-Topaz II
terryhendicott21-Topaz II
21-Topaz II
October 13, 2019

Hi,

 

It is not really a bug, but a matter of internal precision representation of 0.07 / 0.01 being greater than 7.0000000000000000.

Capture.JPG

Cheers

    W
    Werner_E25-Diamond I
    25-Diamond I
    October 13, 2019
    @terryhendicott wrote:

    Hi,

     

    It is not really a bug, but a matter of internal precision representation

    Guess thats exactly what I wrote above when I mentioned the round-off errors due to conversion from decimal to binary and back (in conjunction with the IEEE format used for internal storage).

    The bug is not the lack of precision but the fact, that functions like "Floor" should nonetheless give the correct results with the values shown.

    I agree its not a bug as in both versions, real Mathcad and Prime, we have the options to turn off "exact" comparison (as shown in my other answers) and that way get the correct results.

    W
    Werner_E25-Diamond I
    25-Diamond I
    October 13, 2019

    It gets even more crazy!

    I open the MC11 file which Luc had attached and opened it with MC15.

    As you can see in the screen shot - all calculations are correct now!

    Even if I retype from scratch one of the expressions which formerly gave a wrong result, the result now is correct!!

    When I open an new sheet and copy the region with the correct result from Luc's sheet to the new one, I get the wrong result again.

    My test expression was floor(2.9/0.1) which gives 29 in Luc's sheet and 28 in a sheet created with MC15.

    I also saved Luc's sheet with MC15 in xmcdz format and then reloaded it, but the results still are correct!

     

    EDIT: Found it!! Silly me - I really should have thought on that from the very beginning!

    In real Mathcad one can influence the calculation behavior and in Lucs Sheet in the Worksheet Options the option "Use exact equality for comparison and truncation" was unchecked, while in my sheet this by default was checked.

    Unchecking this options makes sense, I guess.

    clipboard_image_0.png

     

     

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    October 14, 2019

    Mathcad 11 gives me these options:

    clipboard_image_0.png

    The setting that comes closest to Mathcad 15's "Use exact equality for comparison and truncation"  is the last box: "Use exact equality foor boolean comparisons"

    Of course I've tried it. There's no difference in any of the results. Checked or unchecked, I get:

    clipboard_image_1.png

    I've saved the file now with the box checked. Please check how it translates to Mathcad 15..

     

    Luc

    W
    Werner_E25-Diamond I
    25-Diamond I
    October 15, 2019

    Here is what I see when I open your new sheet.

    The box is still checked and some results of course are wrong. Unchecking the box talks Mathcad into delivering correct results.

    clipboard_image_0.png

    W
    Werner_E25-Diamond IAnswer
    25-Diamond I
    October 13, 2019

    The solution is simple.

    Check "Approximate Equality" ("Calculation" ribbon, "Calculation Options") and you should get the correct result:

    clipboard_image_0.png

    clipboard_image_0.png

      A
      Alvaro_951-VisitorAuthor
      1-Visitor
      October 15, 2019

      Very helpful! Thank you Werner. This at least hide the precision error from Mathcad.

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