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15

4

>>> from numpy import inf, nan
>>> z = (inf+0j)*1
(inf+nanj)

Why? This caused a nasty bug in my code.

Why isn't 1 the multiplicative identity, giving (inf + 0j)?

python numpy nan ieee-754

share|improve this question

edited 11 mins ago

Peter Cordes

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asked 10 hours ago

marnixmarnix

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add a comment
 | 

15

4

>>> from numpy import inf, nan
>>> z = (inf+0j)*1
(inf+nanj)

Why? This caused a nasty bug in my code.

Why isn't 1 the multiplicative identity, giving (inf + 0j)?

python numpy nan ieee-754

share|improve this question

edited 11 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 10 hours ago

marnixmarnix

10766 bronze badges

add a comment
 | 

>>> from numpy import inf, nan
>>> z = (inf+0j)*1
(inf+nanj)

Why? This caused a nasty bug in my code.

Why isn't 1 the multiplicative identity, giving (inf + 0j)?

python numpy nan ieee-754

share|improve this question

edited 11 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 10 hours ago

marnixmarnix

10766 bronze badges

>>> from numpy import inf, nan
>>> z = (inf+0j)*1
(inf+nanj)

share|improve this question

edited 11 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 10 hours ago

marnixmarnix

10766 bronze badges

share|improve this question

edited 11 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 10 hours ago

marnixmarnix

10766 bronze badges

edited 11 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

edited 11 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 10 hours ago

marnixmarnix

10766 bronze badges

asked 10 hours ago

marnixmarnix

10766 bronze badges

2 Answers
2

active

oldest

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19

The 1 is converted to a complex number first, 1 + 0j, which then leads to an inf * 0 multiplication, resulting in a nan.

(inf + 0j) * 1
(inf + 0j) * (1 + 0j)
inf * 1 + inf * 0j + 0j * 1 + 0j * 0j
# ^ this is where it comes from
inf + nan j + 0j + 0
inf + nan j

share|improve this answer

edited 10 hours ago

Engineero

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answered 10 hours ago

MaratMarat

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• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  For answering the question "why...?", probably the important most step is the first one, where 1 is cast to 1 + 0j.
  
  – Warren Weckesser
  10 hours ago
  
  

  
  
  
  

add a comment
 | 

-2

To find the "true" reason---as opposed to the purely mechanical reason given in the accepted answer---one probably has to start with something like https://math.stackexchange.com/q/628947

---

A previous version of the question title was worded "Why is (inf + 0j)*1 == inf + nanj?"

That is not in fact the case because nan == nan is false:

from math import inf
(inf+0j)*1==complex("inf+nanj")
# False

share|improve this answer

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

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• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Yeah, because nan != nan. I understand that this answer is half-joking, but I fail to see why it should be helpful to the OP the way it's written.
  
  – cmaster
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why don't you heros take a step back and ask yourselves why you seem uncapable of venting your righteous indignation without patronizing the OP? And if---one may hope---you come to conclude it is yourself who do not follow, there is no shame in asking.
  
  – Paul Panzer
  20 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Given that the code in the question body wasn't actually using == (and given they accepted the other answer), it seems it was just a problem of how the OP expressed the title. I reworded the title to fix that inconsistency. (Intentionally invaliding the first half of this answer because I agree with @cmaster: that isn't what this question was asking about).
  
  – Peter Cordes
  8 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is there a multiplicative identity for complex numbers that does work on inf + 0j?
  
  – Peter Cordes
  4 mins ago
  

  
  
  
  

add a comment
 | 

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19

The 1 is converted to a complex number first, 1 + 0j, which then leads to an inf * 0 multiplication, resulting in a nan.

(inf + 0j) * 1
(inf + 0j) * (1 + 0j)
inf * 1 + inf * 0j + 0j * 1 + 0j * 0j
# ^ this is where it comes from
inf + nan j + 0j + 0
inf + nan j

share|improve this answer

edited 10 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 10 hours ago

MaratMarat

4,96711 gold badge2020 silver badges3434 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  For answering the question "why...?", probably the important most step is the first one, where 1 is cast to 1 + 0j.
  
  – Warren Weckesser
  10 hours ago
  
  

  
  
  
  

add a comment
 | 

19

The 1 is converted to a complex number first, 1 + 0j, which then leads to an inf * 0 multiplication, resulting in a nan.

(inf + 0j) * 1
(inf + 0j) * (1 + 0j)
inf * 1 + inf * 0j + 0j * 1 + 0j * 0j
# ^ this is where it comes from
inf + nan j + 0j + 0
inf + nan j

share|improve this answer

edited 10 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 10 hours ago

MaratMarat

4,96711 gold badge2020 silver badges3434 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  For answering the question "why...?", probably the important most step is the first one, where 1 is cast to 1 + 0j.
  
  – Warren Weckesser
  10 hours ago
  
  

  
  
  
  

add a comment
 | 

The 1 is converted to a complex number first, 1 + 0j, which then leads to an inf * 0 multiplication, resulting in a nan.

(inf + 0j) * 1
(inf + 0j) * (1 + 0j)
inf * 1 + inf * 0j + 0j * 1 + 0j * 0j
# ^ this is where it comes from
inf + nan j + 0j + 0
inf + nan j

share|improve this answer

edited 10 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 10 hours ago

MaratMarat

4,96711 gold badge2020 silver badges3434 bronze badges

(inf + 0j) * 1
(inf + 0j) * (1 + 0j)
inf * 1 + inf * 0j + 0j * 1 + 0j * 0j
# ^ this is where it comes from
inf + nan j + 0j + 0
inf + nan j

share|improve this answer

edited 10 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 10 hours ago

MaratMarat

4,96711 gold badge2020 silver badges3434 bronze badges

edited 10 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

edited 10 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 10 hours ago

MaratMarat

4,96711 gold badge2020 silver badges3434 bronze badges

answered 10 hours ago

MaratMarat

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-2

To find the "true" reason---as opposed to the purely mechanical reason given in the accepted answer---one probably has to start with something like https://math.stackexchange.com/q/628947

---

A previous version of the question title was worded "Why is (inf + 0j)*1 == inf + nanj?"

That is not in fact the case because nan == nan is false:

from math import inf
(inf+0j)*1==complex("inf+nanj")
# False

share|improve this answer

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

35.6k22 gold badges2323 silver badges5454 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Yeah, because nan != nan. I understand that this answer is half-joking, but I fail to see why it should be helpful to the OP the way it's written.
  
  – cmaster
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why don't you heros take a step back and ask yourselves why you seem uncapable of venting your righteous indignation without patronizing the OP? And if---one may hope---you come to conclude it is yourself who do not follow, there is no shame in asking.
  
  – Paul Panzer
  20 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Given that the code in the question body wasn't actually using == (and given they accepted the other answer), it seems it was just a problem of how the OP expressed the title. I reworded the title to fix that inconsistency. (Intentionally invaliding the first half of this answer because I agree with @cmaster: that isn't what this question was asking about).
  
  – Peter Cordes
  8 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is there a multiplicative identity for complex numbers that does work on inf + 0j?
  
  – Peter Cordes
  4 mins ago
  

  
  
  
  

add a comment
 | 

-2

To find the "true" reason---as opposed to the purely mechanical reason given in the accepted answer---one probably has to start with something like https://math.stackexchange.com/q/628947

---

A previous version of the question title was worded "Why is (inf + 0j)*1 == inf + nanj?"

That is not in fact the case because nan == nan is false:

from math import inf
(inf+0j)*1==complex("inf+nanj")
# False

share|improve this answer

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

35.6k22 gold badges2323 silver badges5454 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Yeah, because nan != nan. I understand that this answer is half-joking, but I fail to see why it should be helpful to the OP the way it's written.
  
  – cmaster
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why don't you heros take a step back and ask yourselves why you seem uncapable of venting your righteous indignation without patronizing the OP? And if---one may hope---you come to conclude it is yourself who do not follow, there is no shame in asking.
  
  – Paul Panzer
  20 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Given that the code in the question body wasn't actually using == (and given they accepted the other answer), it seems it was just a problem of how the OP expressed the title. I reworded the title to fix that inconsistency. (Intentionally invaliding the first half of this answer because I agree with @cmaster: that isn't what this question was asking about).
  
  – Peter Cordes
  8 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is there a multiplicative identity for complex numbers that does work on inf + 0j?
  
  – Peter Cordes
  4 mins ago
  

  
  
  
  

add a comment
 | 

To find the "true" reason---as opposed to the purely mechanical reason given in the accepted answer---one probably has to start with something like https://math.stackexchange.com/q/628947

---

A previous version of the question title was worded "Why is (inf + 0j)*1 == inf + nanj?"

That is not in fact the case because nan == nan is false:

from math import inf
(inf+0j)*1==complex("inf+nanj")
# False

share|improve this answer

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

35.6k22 gold badges2323 silver badges5454 bronze badges

from math import inf
(inf+0j)*1==complex("inf+nanj")
# False

share|improve this answer

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

35.6k22 gold badges2323 silver badges5454 bronze badges

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

edited 6 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

35.6k22 gold badges2323 silver badges5454 bronze badges

answered 9 hours ago

Paul PanzerPaul Panzer

35.6k22 gold badges2323 silver badges5454 bronze badges