"Redundant equation" is a MetaPost bug in MkIV?

"Redundant equation" is a MetaPost bug in MkIV?

[Li Yanrui (李延瑞)]

Hi,

See the following example:

\starttext
\startMPcode
u = 1cm;
xmin = -2.6u;
xmax = 4u;
drawarrow (xmin,0)--(xmax,0);
\stopMPcode
\stoptext

It can be compiled rightly. But when I add the 'label' line into it, see:

\starttext
\startMPcode
u = 1cm;
xmin = -2.6u;
xmax = 4u;
drawarrow (xmin,0)--(xmax,0);
label.lft("hello",(0, 0));
\stopMPcode
\stoptext

Now it can not be compiled and luatex outputs:

mplib           : loading 'metafun.mp' (experimental metapost version two)
mplib           > mp terminal: ! Redundant equation.
<to be read again>
                   ;
<*> u = 1cm;
             xmin = -2.6u; xmax = 4u; drawarrow (xmin,0)--(xmax,0); label.lf...

! Redundant equation.
<to be read again>

Is this a bug or it always need to use 'save' macro to hold these
local variable in metafun?

-- 
Best regards,

Li Yanrui
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___________________________________________________________________________________

Re: "Redundant equation" is a MetaPost bug in MkIV?

[Aditya Mahajan]

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On Sun, 5 Dec 2010, Li Yanrui (李延瑞) wrote:

> Hi,
>
> See the following example:
>
> \starttext
> \startMPcode
> u = 1cm;
> xmin = -2.6u;
> xmax = 4u;
> drawarrow (xmin,0)--(xmax,0);
> \stopMPcode
> \stoptext
>
> It can be compiled rightly. But when I add the 'label' line into it, see:
>
> \starttext
> \startMPcode
> u = 1cm;
> xmin = -2.6u;
> xmax = 4u;
> drawarrow (xmin,0)--(xmax,0);
> label.lft("hello",(0, 0));
> \stopMPcode
> \stoptext
>
> Now it can not be compiled and luatex outputs:
>
> mplib           : loading 'metafun.mp' (experimental metapost version two)
> mplib           > mp terminal: ! Redundant equation.
> <to be read again>
>                   ;
> <*> u = 1cm;
>             xmin = -2.6u; xmax = 4u; drawarrow (xmin,0)--(xmax,0); label.lf...
>
> ! Redundant equation.
> <to be read again>
>
> Is this a bug or it always need to use 'save' macro to hold these
> local variable in metafun?

When a label (or btex ... etex) is present, ConTeXt processes the MP code 
twice: once to typeset the labels and then to place to labels. You get a 
redundant equation in the second pass.

The easiest way to prevent this is to use := instead of =

Aditya

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Re: "Redundant equation" is a MetaPost bug in MkIV?

[Taco Hoekwater]

On 12/05/2010 04:14 AM, Li Yanrui (李延瑞) wrote:
>
> Is this a bug or it always need to use 'save' macro to hold these
> local variable in metafun?

It is a side-effect of MkIV running your code through metapost
multiple times. But why it does that, I am not sure.

Best wishes,
Taco
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Re: "Redundant equation" is a MetaPost bug in MkIV?

[Yury G. Kudryashov]

Li Yanrui (李延瑞) wrote:

> Hi,
> 
> Now it can not be compiled and luatex outputs:
> 
> mplib           : loading 'metafun.mp' (experimental metapost version two)
> mplib           > mp terminal: ! Redundant equation.
> <to be read again>
>                    ;
> <*> u = 1cm;
>              xmin = -2.6u; xmax = 4u; drawarrow (xmin,0)--(xmax,0);
>              label.lf...
> 
> ! Redundant equation.
> <to be read again>
> 
> Is this a bug or it always need to use 'save' macro to hold these
> local variable in metafun?
ConTeXt compiles all metapost code in one long run, so you have to re-
declare 'u' to avoid this error (e.g. 'save' or 'numeric u;').


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___________________________________________________________________________________

Re: "Redundant equation" is a MetaPost bug in MkIV?

[Alan BRASLAU]

Hello,

You should change all of the "=" to ":=", as in
u := 1cm;

This instructs metapost to assign a value to the variable;
the standard form "u = 1cm" is a formula for metapost to solve.
It tries then to resolve u = 1cm; xmin = -2.6u; and xmax = 4u;
as a coupled set of equations. Sometimes you can get away with
this but in general one should use the := (assignment) form.

Consider, for example:
u = u + 1;
(a standard programming statement but nonsense for a mathematician).

Alan



On Sunday 05 December 2010 04:14:01 Li Yanrui (李延瑞) wrote:
> Hi,
> 
> See the following example:
> 
> \starttext
> \startMPcode
> u = 1cm;
> xmin = -2.6u;
> xmax = 4u;
> drawarrow (xmin,0)--(xmax,0);
> \stopMPcode
> \stoptext
> 
> It can be compiled rightly. But when I add the 'label' line into it, see:
> 
> \starttext
> \startMPcode
> u = 1cm;
> xmin = -2.6u;
> xmax = 4u;
> drawarrow (xmin,0)--(xmax,0);
> label.lft("hello",(0, 0));
> \stopMPcode
> \stoptext
> 
> Now it can not be compiled and luatex outputs:
> 
> mplib           : loading 'metafun.mp' (experimental metapost version two)
> mplib           > mp terminal: ! Redundant equation.
> <to be read again>
>                    ;
> <*> u = 1cm;
>              xmin = -2.6u; xmax = 4u; drawarrow (xmin,0)--(xmax,0);
> label.lf...
> 
> ! Redundant equation.
> <to be read again>
> 
> Is this a bug or it always need to use 'save' macro to hold these
> local variable in metafun?
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
archive  : http://foundry.supelec.fr/projects/contextrev/
wiki     : http://contextgarden.net
___________________________________________________________________________________

Re: "Redundant equation" is a MetaPost bug in MkIV?

[Li Yanrui (李延瑞)]

2010/12/5 Alan BRASLAU <alan.braslau@cea.fr>:
> Hello,
>
> You should change all of the "=" to ":=", as in
> u := 1cm;
>
> This instructs metapost to assign a value to the variable;
> the standard form "u = 1cm" is a formula for metapost to solve.
> It tries then to resolve u = 1cm; xmin = -2.6u; and xmax = 4u;
> as a coupled set of equations. Sometimes you can get away with
> this but in general one should use the := (assignment) form.
>
> Consider, for example:
> u = u + 1;
> (a standard programming statement but nonsense for a mathematician).
>

I know the difference between "=" and ":=". But that example shows the
metafun in MkIV is abnormal since it can be compiled rightly in MkII,
which should not have any syntax error.

In fact, the following example can be compiled rightly in MkIV.

\starttext
\startMPcode
save u, xmin, xmax;
u = 1cm;
xmin = -2.6u;
xmax = 4u;
drawarrow (xmin,0)--(xmax,0);
label.lft("hello",(0, 0));
\stopMPcode
\stoptext

-- 
Best regards,

Li Yanrui (李延瑞)
___________________________________________________________________________________
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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
archive  : http://foundry.supelec.fr/projects/contextrev/
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___________________________________________________________________________________

Re: "Redundant equation" is a MetaPost bug in MkIV?

[Li Yanrui (李延瑞)]

2010/12/5 Aditya Mahajan <adityam@umich.edu>:
> On Sun, 5 Dec 2010, Li Yanrui (李延瑞) wrote:
>
> When a label (or btex ... etex) is present, ConTeXt processes the MP code
> twice: once to typeset the labels and then to place to labels. You get a
> redundant equation in the second pass.
>
> The easiest way to prevent this is to use := instead of =
>

I see now. Thank you Aditya and others !

-- 
Best regards,

Li Yanrui
___________________________________________________________________________________
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maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
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archive  : http://foundry.supelec.fr/projects/contextrev/
wiki     : http://contextgarden.net
___________________________________________________________________________________