Incorrect result in Shader Node Math.Fraction #107518

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opened 2023-05-01 23:48:20 +02:00 by Vladimir · 8 comments

Vladimir commented

2023-05-01 23:48:20 +02:00

System Information
Operating system: Linux-6.3.0-1-MANJARO-x86_64-with-glibc2.37 64 Bits, X11 UI
Graphics card: Mesa Intel(R) HD Graphics 4600 (HSW GT2) Intel 4.6 (Core Profile) Mesa 23.0.3

Blender Version
Broken: version: 3.6.0 Alpha, branch: main, commit date: 2023-04-30 05:23, hash: 358ce4f52b58
Worked: (newest version of Blender that worked as expected)

Short description of error

Blender official docs:
https://docs.blender.org/manual/en/latest/modeling/geometry_nodes/utilities/math.html
Fraction - Returns the fractional part of the value.

When I input float value equals 12.56 into Fraction, return 0.56, it is ok. But when I input a value equals -12.56 (negative sign), Fraction return value 0.43 !!!

Exact steps for others to reproduce the error

**System Information** Operating system: Linux-6.3.0-1-MANJARO-x86_64-with-glibc2.37 64 Bits, X11 UI Graphics card: Mesa Intel(R) HD Graphics 4600 (HSW GT2) Intel 4.6 (Core Profile) Mesa 23.0.3 **Blender Version** Broken: version: 3.6.0 Alpha, branch: main, commit date: 2023-04-30 05:23, hash: `358ce4f52b58` Worked: (newest version of Blender that worked as expected) **Short description of error** Blender official docs: https://docs.blender.org/manual/en/latest/modeling/geometry_nodes/utilities/math.html **Fraction** - Returns the fractional part of the value. When I input float value equals **12.56** into Fraction, return 0.56, it is ok. But when I input a value equals **-12.56** (negative sign), Fraction return value 0.43 !!! ![Screenshot_20230502_002537.png](/attachments/e940a63e-709c-4de6-9faf-5cfa36d44788) **Exact steps for others to reproduce the error**

Math.Fraction.blend

1.2 MiB

Screenshot_20230502_005038.png

98 KiB

Vladimir added the

labels 2023-05-01 23:48:20 +02:00

Iliya Katushenock added the

Nodes & Physics

label 2023-05-02 08:10:26 +02:00

Pratik Borhade commented

2023-05-02 08:37:12 +02:00

Member

Hi, thanks for the report. Don't think this is a bug. For me, this looks expected codewise and conceptwise.
To calculate the decimal part of any real number, the logic is to subtract floor number from the actual number.
i.e. x - floorf(x)
And remainder has to be positive always (if we consider 0.56 as a answer then it will be -0.56 which is incorrect).
Also see: https://math.stackexchange.com/questions/710018/fractional-integer-parts-of-a-negative-real

Will close this report. Feel free to comment if there is any misunderstanding.

Hi, thanks for the report. Don't think this is a bug. For me, this looks expected codewise and conceptwise. To calculate the decimal part of any real number, the logic is to subtract floor number from the actual number. i.e. x - floorf(x) And remainder has to be positive always (if we consider 0.56 as a answer then it will be -0.56 which is incorrect). Also see: https://math.stackexchange.com/questions/710018/fractional-integer-parts-of-a-negative-real Will close this report. Feel free to comment if there is any misunderstanding.

Pratik Borhade closed this issue

2023-05-02 08:37:14 +02:00

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labels 2023-05-02 08:37:15 +02:00

Vladimir commented

2023-05-02 20:40:01 +02:00

Author

Hi, thanks for the report. Don't think this is a bug. For me, this looks expected codewise and conceptwise.
To calculate the decimal part of any real number, the logic is to subtract floor number from the actual number.
i.e. x - floorf(x)
And remainder has to be positive always (if we consider 0.56 as a answer then it will be -0.56 which is incorrect).
Also see: https://math.stackexchange.com/questions/710018/fractional-integer-parts-of-a-negative-real

Will close this report. Feel free to comment if there is any misunderstanding.

Hi!
I am not programmer, there it is code tier and I am user :) Fraction should be return fraction but not random value. Else, what is fraction?

Python:
math.modf(x)
Return the fractional and integer parts of x. Both results carry the sign of x and are floats.

>>> import math

>>> math.modf(10.5)
(0.5, 10.0)

>>> math.modf(-10.5)
(-0.5, -10.0)

> Hi, thanks for the report. Don't think this is a bug. For me, this looks expected codewise and conceptwise. > To calculate the decimal part of any real number, the logic is to subtract floor number from the actual number. > i.e. x - floorf(x) > And remainder has to be positive always (if we consider 0.56 as a answer then it will be -0.56 which is incorrect). > Also see: https://math.stackexchange.com/questions/710018/fractional-integer-parts-of-a-negative-real > > Will close this report. Feel free to comment if there is any misunderstanding. > Hi! I am not programmer, there it is code tier and I am user :) Fraction should be return fraction but not random value. Else, what is fraction? Python: math.modf(x) Return the fractional and integer parts of x. Both results carry the sign of x and are floats. ```python >>> import math >>> math.modf(10.5) (0.5, 10.0) >>> math.modf(-10.5) (-0.5, -10.0) ```

Vladimir reopened this issue

2023-05-02 20:40:03 +02:00

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labels 2023-05-02 20:40:05 +02:00

Ray molenkamp commented

2023-05-02 21:04:29 +02:00

Member

It's not a random value, the value is explained in the link @PratikPB2123 gave, this definition of fract is quite common in shading languages ie opengl

You get similar behavior in pythons divmod function

>>> divmod(-12.56, 1.0)
(-13.0, 0.4399999999999995)

This is working as designed, not a bug

It's not a random value, the value is explained in the link @PratikPB2123 gave, this definition of fract is quite common in shading languages ie [opengl](https://registry.khronos.org/OpenGL-Refpages/gl4/html/fract.xhtml) You get similar behavior in pythons `divmod` function ``` >>> divmod(-12.56, 1.0) (-13.0, 0.4399999999999995) ``` This is working as designed, not a bug

Ray molenkamp closed this issue

2023-05-02 21:04:31 +02:00

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labels 2023-05-02 21:04:32 +02:00

Vladimir commented

2023-05-02 21:36:18 +02:00

Author

divmod(-12.56, 1.0)
(-13.0, 0.4399999999999995)

This is working as designed, not a bug

Here - yes, as designed because div is division but not fraction:

divmod Description:
Returns quotient and remainder after a division of two numbers.
https://python-reference.readthedocs.io/en/latest/docs/functions/divmod.html

Math.Fraction in Blender has confuse name and also description in docs:

Fraction:
Returns the fractional part of the value.

> >>> divmod(-12.56, 1.0) > (-13.0, 0.4399999999999995) > > > This is working as designed, not a bug Here - yes, as designed because div is division but not fraction: **divmod** Description: Returns quotient and remainder **after a division of two numbers**. https://python-reference.readthedocs.io/en/latest/docs/functions/divmod.html Math.Fraction in Blender has confuse name and also description in docs: >Fraction: > Returns the fractional part of the value.

Vladimir reopened this issue

2023-05-02 21:36:20 +02:00

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labels 2023-05-02 21:36:21 +02:00

Iliya Katushenock commented

2023-05-02 21:42:20 +02:00

Member

![image](/attachments/8a2f6320-6222-42b1-8d46-b4a8f23249aa)

9.5 KiB

Iliya Katushenock closed this issue

2023-05-02 21:42:22 +02:00

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labels 2023-05-02 21:42:23 +02:00

Vladimir commented

2023-05-02 22:08:01 +02:00

Author

I followed that link, nothing understand, only it is stated that the graph is not symmetrical. Moreover, the graph is also not symmetrical in the positive direction, and not only in the negative! That is, it turns out that the Fraction can return strange numbers even with positive input values? o_O

Blender help will be corrected? Need correct description

I followed that link, nothing understand, only it is stated that the graph is not symmetrical. Moreover, the graph is also not symmetrical in the positive direction, and not only in the negative! That is, it turns out that the Fraction can return strange numbers even with positive input values? o_O Blender help will be corrected? Need correct description

Iliya Katushenock commented

2023-05-02 22:13:23 +02:00

Member

I'm still not sure about the substance of the report. This is a normal, old, function. Graphic programming is based on how it works, like noise or texture. This is a very basic thing. And it's definitely not a bug.

I'm still not sure about the substance of the report. This is a normal, old, function. Graphic programming is based on how it works, like noise or texture. This is a very basic thing. And it's definitely not a bug.

Vladimir commented

2023-05-02 22:26:41 +02:00

Author

Thanks for all, guys! :) Sorry... I now understand! :) This link helped me:

https://www.cuemath.com/calculus/fractional-part-function/

i will know now

Thanks for all, guys! :) Sorry... I now understand! :) This link helped me: https://www.cuemath.com/calculus/fractional-part-function/ i will know now

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