`Re[z]` Command [closed]

2

$begingroup$

Suppose we have complex number $z=a+i b$, where $a$ and $b$ are variables.

Now, if we want real part of $z$, then in mathematica we use Re[z] command. But this command is not working (because $a$ and $b$ are not fixed real numbers).

Re[expr] is left unevaluated if expr is not a numeric quantity. (https://reference.wolfram.com/language/ref/Re.html)

How do we get Re[z]$=a$ as solution?

complex

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asked Jan 25 at 15:00

GoldyGoldy

1702

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closed as off-topic by Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march Jan 28 at 18:17

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march

If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  See "Properties & Relations" in the documentation for Re. It shows various uses of ComplexExpand with respect to Re.
  $endgroup$
  – Michael E2
  Jan 25 at 16:56
  

  
  
  
  

add a comment | 

2

$begingroup$

Suppose we have complex number $z=a+i b$, where $a$ and $b$ are variables.

Now, if we want real part of $z$, then in mathematica we use Re[z] command. But this command is not working (because $a$ and $b$ are not fixed real numbers).

Re[expr] is left unevaluated if expr is not a numeric quantity. (https://reference.wolfram.com/language/ref/Re.html)

How do we get Re[z]$=a$ as solution?

complex

share|improve this question

asked Jan 25 at 15:00

GoldyGoldy

1702

$endgroup$

closed as off-topic by Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march Jan 28 at 18:17

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march

If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  See "Properties & Relations" in the documentation for Re. It shows various uses of ComplexExpand with respect to Re.
  $endgroup$
  – Michael E2
  Jan 25 at 16:56
  

  
  
  
  

add a comment | 

2

2

2

$begingroup$

Suppose we have complex number $z=a+i b$, where $a$ and $b$ are variables.

Now, if we want real part of $z$, then in mathematica we use Re[z] command. But this command is not working (because $a$ and $b$ are not fixed real numbers).

Re[expr] is left unevaluated if expr is not a numeric quantity. (https://reference.wolfram.com/language/ref/Re.html)

How do we get Re[z]$=a$ as solution?

complex

share|improve this question

asked Jan 25 at 15:00

GoldyGoldy

1702

$endgroup$

Suppose we have complex number $z=a+i b$, where $a$ and $b$ are variables.

Now, if we want real part of $z$, then in mathematica we use Re[z] command. But this command is not working (because $a$ and $b$ are not fixed real numbers).

Re[expr] is left unevaluated if expr is not a numeric quantity. (https://reference.wolfram.com/language/ref/Re.html)

How do we get Re[z]$=a$ as solution?

complex

complex

share|improve this question

asked Jan 25 at 15:00

GoldyGoldy

1702

share|improve this question

asked Jan 25 at 15:00

GoldyGoldy

1702

share|improve this question

share|improve this question

asked Jan 25 at 15:00

GoldyGoldy

1702

asked Jan 25 at 15:00

GoldyGoldy

1702

asked Jan 25 at 15:00

GoldyGoldy

1702

1702

closed as off-topic by Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march Jan 28 at 18:17

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march

If this question can be reworded to fit the rules in the help center, please edit the question.

closed as off-topic by Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march Jan 28 at 18:17

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – Michael E2, Daniel Lichtblau, b3m2a1, m_goldberg, march

If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  See "Properties & Relations" in the documentation for Re. It shows various uses of ComplexExpand with respect to Re.
  $endgroup$
  – Michael E2
  Jan 25 at 16:56
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  See "Properties & Relations" in the documentation for Re. It shows various uses of ComplexExpand with respect to Re.
  $endgroup$
  – Michael E2
  Jan 25 at 16:56
  

  
  
  
  

3

3

$begingroup$
See "Properties & Relations" in the documentation for Re. It shows various uses of ComplexExpand with respect to Re.
$endgroup$
– Michael E2
Jan 25 at 16:56

$begingroup$
See "Properties & Relations" in the documentation for Re. It shows various uses of ComplexExpand with respect to Re.
$endgroup$
– Michael E2
Jan 25 at 16:56

add a comment | 

2 Answers
2

active

oldest

votes

2

$begingroup$

z = a + I b;

ComplexExpand[Re[z]]

a

Hope that helps.

share|improve this answer

answered Jan 25 at 15:08

HughHugh

6,61921946

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
  $endgroup$
  – Goldy
  Jan 25 at 15:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
  $endgroup$
  – Goldy
  Jan 25 at 15:18
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
  $endgroup$
  – Hugh
  Jan 25 at 15:23
  

  
  
  
  

add a comment | 

3

$begingroup$

The rewrite rules behind ComplexExpand assume all undefined symbols in the expression are real.

ComplexExpand[z]

is just

z

Thus,

Re[ComplexExpand[z]]

first gets rewritten as

Re[z]

and no further rewrite is possible because Re has no rule for this case. But ComplexExpand inspects the structure of the expression it's given. It recognizes that it can rewrite Re[z] as z.

Mathematica is a language for rewriting mathematical expressions based on recognizing their structure. Sometimes those rewrites seem to act like "commands", but it is misleading to think of them that way.

share|improve this answer

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

$endgroup$

add a comment | 

2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

2

$begingroup$

z = a + I b;

ComplexExpand[Re[z]]

a

Hope that helps.

share|improve this answer

answered Jan 25 at 15:08

HughHugh

6,61921946

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
  $endgroup$
  – Goldy
  Jan 25 at 15:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
  $endgroup$
  – Goldy
  Jan 25 at 15:18
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
  $endgroup$
  – Hugh
  Jan 25 at 15:23
  

  
  
  
  

add a comment | 

2

$begingroup$

z = a + I b;

ComplexExpand[Re[z]]

a

Hope that helps.

share|improve this answer

answered Jan 25 at 15:08

HughHugh

6,61921946

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
  $endgroup$
  – Goldy
  Jan 25 at 15:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
  $endgroup$
  – Goldy
  Jan 25 at 15:18
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
  $endgroup$
  – Hugh
  Jan 25 at 15:23
  

  
  
  
  

add a comment | 

2

2

2

$begingroup$

z = a + I b;

ComplexExpand[Re[z]]

a

Hope that helps.

share|improve this answer

answered Jan 25 at 15:08

HughHugh

6,61921946

$endgroup$

z = a + I b;

ComplexExpand[Re[z]]

a

Hope that helps.

share|improve this answer

answered Jan 25 at 15:08

HughHugh

6,61921946

share|improve this answer

share|improve this answer

answered Jan 25 at 15:08

HughHugh

6,61921946

answered Jan 25 at 15:08

HughHugh

6,61921946

answered Jan 25 at 15:08

HughHugh

6,61921946

6,61921946

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
  $endgroup$
  – Goldy
  Jan 25 at 15:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
  $endgroup$
  – Goldy
  Jan 25 at 15:18
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
  $endgroup$
  – Hugh
  Jan 25 at 15:23
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
  $endgroup$
  – Goldy
  Jan 25 at 15:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
  $endgroup$
  – Goldy
  Jan 25 at 15:18
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
  $endgroup$
  – Hugh
  Jan 25 at 15:23
  

  
  
  
  

$begingroup$
But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
$endgroup$
– Goldy
Jan 25 at 15:17

$begingroup$
But what is the difference between ComplexExpand[Re[z]] and Re[ComplexExpand[z]]??
$endgroup$
– Goldy
Jan 25 at 15:17

$begingroup$
Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
$endgroup$
– Goldy
Jan 25 at 15:18

$begingroup$
Command ComplexExpand[Re[z]] gives me correct result, but Re[ComplexExpand[z]] is not working
$endgroup$
– Goldy
Jan 25 at 15:18

1

1

$begingroup$
ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
$endgroup$
– Hugh
Jan 25 at 15:23

$begingroup$
ComplexExpand[z] has not got any work to do. If you try ComplexExpand[z^2] then it does do some work. Have a good look at the documentation. What would you expect it to do?
$endgroup$
– Hugh
Jan 25 at 15:23

add a comment | 

3

$begingroup$

The rewrite rules behind ComplexExpand assume all undefined symbols in the expression are real.

ComplexExpand[z]

is just

z

Thus,

Re[ComplexExpand[z]]

first gets rewritten as

Re[z]

and no further rewrite is possible because Re has no rule for this case. But ComplexExpand inspects the structure of the expression it's given. It recognizes that it can rewrite Re[z] as z.

Mathematica is a language for rewriting mathematical expressions based on recognizing their structure. Sometimes those rewrites seem to act like "commands", but it is misleading to think of them that way.

share|improve this answer

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

$endgroup$

add a comment | 

3

$begingroup$

The rewrite rules behind ComplexExpand assume all undefined symbols in the expression are real.

ComplexExpand[z]

is just

z

Thus,

Re[ComplexExpand[z]]

first gets rewritten as

Re[z]

and no further rewrite is possible because Re has no rule for this case. But ComplexExpand inspects the structure of the expression it's given. It recognizes that it can rewrite Re[z] as z.

Mathematica is a language for rewriting mathematical expressions based on recognizing their structure. Sometimes those rewrites seem to act like "commands", but it is misleading to think of them that way.

share|improve this answer

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

$endgroup$

add a comment | 

3

3

3

$begingroup$

The rewrite rules behind ComplexExpand assume all undefined symbols in the expression are real.

ComplexExpand[z]

is just

z

Thus,

Re[ComplexExpand[z]]

first gets rewritten as

Re[z]

and no further rewrite is possible because Re has no rule for this case. But ComplexExpand inspects the structure of the expression it's given. It recognizes that it can rewrite Re[z] as z.

Mathematica is a language for rewriting mathematical expressions based on recognizing their structure. Sometimes those rewrites seem to act like "commands", but it is misleading to think of them that way.

share|improve this answer

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

$endgroup$

The rewrite rules behind ComplexExpand assume all undefined symbols in the expression are real.

ComplexExpand[z]

is just

z

Thus,

Re[ComplexExpand[z]]

first gets rewritten as

Re[z]

and no further rewrite is possible because Re has no rule for this case. But ComplexExpand inspects the structure of the expression it's given. It recognizes that it can rewrite Re[z] as z.

Mathematica is a language for rewriting mathematical expressions based on recognizing their structure. Sometimes those rewrites seem to act like "commands", but it is misleading to think of them that way.

share|improve this answer

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

share|improve this answer

share|improve this answer

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

answered Jan 25 at 15:30

John DotyJohn Doty

7,38311124

7,38311124

add a comment | 

add a comment | 

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