Mdthbs

Is "ln" (natural log) and "log" the same thing if used in this answer?

How to deal with my team leader who keeps calling me about project updates even though I am on leave for personal reasons?

What is the need of methods like GET and POST in the HTTP protocol?

Is it impolite to ask for an in-flight catalogue with no intention of buying?

Does the Prepare Food ability from Cook's Utensils stack?

Cut a cake into 3 equal portions with only a knife

Could Apollo astronauts see city lights from the moon?

Extruding snaps back

How can this Stack Exchange site have an animated favicon?

Do we have any particular tonal center in mind when we are NOT listening music?

Safely hang a mirror that does not have hooks

Should the average user with no special access rights be worried about SMS-based 2FA being theoretically interceptable?

When is it acceptable to write a bad letter of recommendation?

Designing a time thief proof safe

Social leper versus social leopard

2000s Animated TV show where teenagers could physically go into a virtual world

What secular civic space would pioneers build for small frontier towns?

Guitar tuning (EADGBE), "perfect" fourths?

If an object moving in a circle experiences centripetal force, then doesn't it also experience centrifugal force, because of Newton's third law?

A food item only made possible by time-freezing storage?

Going to France with limited French for a day

What can a pilot do if an air traffic controller is incapacitated?

Meaning of 'ran' in German?

while loop factorial only works up to 20?

Why does (inf + 0j)*1 evaluate to inf + nanj?

What does ** (double star/asterisk) and * (star/asterisk) do for parameters?What does the “yield” keyword do?Does Python have a ternary conditional operator?What does if __name__ == “__main__”: do?Python join: why is it string.join(list) instead of list.join(string)?What is the rationale for all comparisons returning false for IEEE754 NaN values?Does Python have a string 'contains' substring method?Why is reading lines from stdin much slower in C++ than Python?Why is “1000000000000000 in range(1000000000000001)” so fast in Python 3?

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}

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 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 11 hours ago

marnixmarnix

10766 bronze badges

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 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 11 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 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 11 hours ago

marnixmarnix

10766 bronze badges

>>> from numpy import inf, nan

>>> z = (inf+0j)*1

(inf+nanj)

share|improve this question

edited 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 11 hours ago

marnixmarnix

10766 bronze badges

share|improve this question

edited 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 11 hours ago

marnixmarnix

10766 bronze badges

edited 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

edited 57 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

asked 11 hours ago

marnixmarnix

10766 bronze badges

asked 11 hours ago

marnixmarnix

10766 bronze badges

2 Answers
2

active

oldest

votes

20

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 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 11 hours ago

MaratMarat

4,97711 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
  11 hours ago
  
  
  

  
  
  
  

add a comment
 | 

-4

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 52 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

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  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
  3 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
  1 hour 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
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

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

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @PeterCordes that would be troubling because using polar coordinates we can view complex multiplication as a scaling and a rotation. Rotating an infinite "arm" even by 0 degrees as in the case of multiplying by one we cannot expect to place its tip with finite precision. This is in my opinion a deeper explanation than the accepted one, and also one with echos in the nan != nan rule.
  
  – Paul Panzer
  35 mins ago
  

  
  
  
  

add a comment
 | 

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/4.0/"u003ecc by-sa 4.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f58031966%2fwhy-does-inf-0j1-evaluate-to-inf-nanj%23new-answer', 'question_page');
}
);

Post as a guest

Name

Email

Required, but never shown

20

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 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 11 hours ago

MaratMarat

4,97711 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
  11 hours ago
  
  
  

  
  
  
  

add a comment
 | 

20

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 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 11 hours ago

MaratMarat

4,97711 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
  11 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 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 11 hours ago

MaratMarat

4,97711 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 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 11 hours ago

MaratMarat

4,97711 gold badge2020 silver badges3434 bronze badges

edited 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

edited 11 hours ago

Engineero

7,35433 gold badges2626 silver badges5252 bronze badges

answered 11 hours ago

MaratMarat

4,97711 gold badge2020 silver badges3434 bronze badges

answered 11 hours ago

MaratMarat

4,97711 gold badge2020 silver badges3434 bronze badges

-4

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 52 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

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  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
  3 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
  1 hour 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
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

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

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @PeterCordes that would be troubling because using polar coordinates we can view complex multiplication as a scaling and a rotation. Rotating an infinite "arm" even by 0 degrees as in the case of multiplying by one we cannot expect to place its tip with finite precision. This is in my opinion a deeper explanation than the accepted one, and also one with echos in the nan != nan rule.
  
  – Paul Panzer
  35 mins ago
  

  
  
  
  

add a comment
 | 

-4

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 52 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

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  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
  3 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
  1 hour 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
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

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

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @PeterCordes that would be troubling because using polar coordinates we can view complex multiplication as a scaling and a rotation. Rotating an infinite "arm" even by 0 degrees as in the case of multiplying by one we cannot expect to place its tip with finite precision. This is in my opinion a deeper explanation than the accepted one, and also one with echos in the nan != nan rule.
  
  – Paul Panzer
  35 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 52 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 52 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 52 mins ago

Peter Cordes

158k2323 gold badges254254 silver badges406406 bronze badges

edited 52 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