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Why does this syntax outputs an error under METAFUN/METAPOST?

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

2

Given this MWE (compiled under ConTeXt)

starttext

startMPpage



%variables

u:=1mm ;

numeric l[];

l[1]:=30 ;

l[2]:=70 ;



draw (0,0) -- (0,100u) ;

%this does not work

%fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;



%this does

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100u shifted (l[1]*u,0) withcolor red ;



stopMPpage

stoptext

Could you explain me why

fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;

fails, whereas

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100*u shifted (l[1]*u,0) withcolor red ;

does the job?

From my (not so good in maths) points of view, (l[2]-l[1])*u should be exactly the same, and this misunderstandings leads me often to frustrating errors.

I hope this is not a duplicate, but didn't know how to produce a proper title.

metapost metafun

share|improve this question

edited 9 hours ago

sztruks

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Have you tried xscaled ((l[2]-l[1])*u)?
  
  – Ruixi Zhang
  9 hours ago
  

  
  
  
  

add a comment | 

2

Given this MWE (compiled under ConTeXt)

starttext

startMPpage



%variables

u:=1mm ;

numeric l[];

l[1]:=30 ;

l[2]:=70 ;



draw (0,0) -- (0,100u) ;

%this does not work

%fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;



%this does

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100u shifted (l[1]*u,0) withcolor red ;



stopMPpage

stoptext

Could you explain me why

fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;

fails, whereas

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100*u shifted (l[1]*u,0) withcolor red ;

does the job?

From my (not so good in maths) points of view, (l[2]-l[1])*u should be exactly the same, and this misunderstandings leads me often to frustrating errors.

I hope this is not a duplicate, but didn't know how to produce a proper title.

metapost metafun

share|improve this question

edited 9 hours ago

sztruks

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Have you tried xscaled ((l[2]-l[1])*u)?
  
  – Ruixi Zhang
  9 hours ago
  

  
  
  
  

add a comment | 

Given this MWE (compiled under ConTeXt)

starttext

startMPpage



%variables

u:=1mm ;

numeric l[];

l[1]:=30 ;

l[2]:=70 ;



draw (0,0) -- (0,100u) ;

%this does not work

%fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;



%this does

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100u shifted (l[1]*u,0) withcolor red ;



stopMPpage

stoptext

Could you explain me why

fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;

fails, whereas

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100*u shifted (l[1]*u,0) withcolor red ;

does the job?

From my (not so good in maths) points of view, (l[2]-l[1])*u should be exactly the same, and this misunderstandings leads me often to frustrating errors.

I hope this is not a duplicate, but didn't know how to produce a proper title.

metapost metafun

share|improve this question

edited 9 hours ago

sztruks

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

starttext

startMPpage



%variables

u:=1mm ;

numeric l[];

l[1]:=30 ;

l[2]:=70 ;



draw (0,0) -- (0,100u) ;

%this does not work

%fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;



%this does

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100u shifted (l[1]*u,0) withcolor red ;



stopMPpage

stoptext

fill unitsquare xscaled (l[2]-l[1])*u yscaled 100*u shifted (l[1]*u,0) withcolor red ;

fill unitsquare xscaled (l[2]*u-l[1]*u) yscaled 100*u shifted (l[1]*u,0) withcolor red ;

share|improve this question

edited 9 hours ago

sztruks

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

share|improve this question

edited 9 hours ago

sztruks

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

asked 10 hours ago

sztrukssztruks

1,74311 gold badge88 silver badges1717 bronze badges

1 Answer
1

active

oldest

votes

5

According to the Metapost manual, xscaled is a primary, so it has the same priority as multiplication.

It takes as arguments a pair, path or picture and a number, returning a pair, path or picture respectively; with your “non working” syntax Metapost is doing

unitsquare xscaled (l[2]-l[1])

and then trying to multiply the result by u, which is an invalid operation.

When operations have the same priority (all primaries, for instance), Metapost associates on the left. To get a different association you need parentheses.

The error you get is

>> path

>> 2.83464

! Not implemented: (path)*(known numeric).

<to be read again> 

                   yscaled

Of course ((l[2]-l[1])*u) would work as well, but the outer parentheses cannot be omitted.

share|improve this answer

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges

add a comment | 

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5

According to the Metapost manual, xscaled is a primary, so it has the same priority as multiplication.

It takes as arguments a pair, path or picture and a number, returning a pair, path or picture respectively; with your “non working” syntax Metapost is doing

unitsquare xscaled (l[2]-l[1])

and then trying to multiply the result by u, which is an invalid operation.

When operations have the same priority (all primaries, for instance), Metapost associates on the left. To get a different association you need parentheses.

The error you get is

>> path

>> 2.83464

! Not implemented: (path)*(known numeric).

<to be read again> 

                   yscaled

Of course ((l[2]-l[1])*u) would work as well, but the outer parentheses cannot be omitted.

share|improve this answer

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges

add a comment | 

5

According to the Metapost manual, xscaled is a primary, so it has the same priority as multiplication.

It takes as arguments a pair, path or picture and a number, returning a pair, path or picture respectively; with your “non working” syntax Metapost is doing

unitsquare xscaled (l[2]-l[1])

and then trying to multiply the result by u, which is an invalid operation.

When operations have the same priority (all primaries, for instance), Metapost associates on the left. To get a different association you need parentheses.

The error you get is

>> path

>> 2.83464

! Not implemented: (path)*(known numeric).

<to be read again> 

                   yscaled

Of course ((l[2]-l[1])*u) would work as well, but the outer parentheses cannot be omitted.

share|improve this answer

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges

add a comment | 

According to the Metapost manual, xscaled is a primary, so it has the same priority as multiplication.

It takes as arguments a pair, path or picture and a number, returning a pair, path or picture respectively; with your “non working” syntax Metapost is doing

unitsquare xscaled (l[2]-l[1])

and then trying to multiply the result by u, which is an invalid operation.

When operations have the same priority (all primaries, for instance), Metapost associates on the left. To get a different association you need parentheses.

The error you get is

>> path

>> 2.83464

! Not implemented: (path)*(known numeric).

<to be read again> 

                   yscaled

Of course ((l[2]-l[1])*u) would work as well, but the outer parentheses cannot be omitted.

share|improve this answer

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges

unitsquare xscaled (l[2]-l[1])

>> path

>> 2.83464

! Not implemented: (path)*(known numeric).

<to be read again> 

                   yscaled

share|improve this answer

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges

answered 9 hours ago

egregegreg

766k9090 gold badges19991999 silver badges33513351 bronze badges