UsingWW: Kenneth Appel - TeX and Matrices

$inactiveTopic$ TeX and Matrices

topic started 11/19/2004; 3:34:33 PM
last post 11/22/2004; 12:27:35 PM

$user$ Kenneth Appel - TeX and Matrices $blueArrow$
11/19/2004; 3:34:33 PM (reads: 3379, responses: 8)

I would appreciate any explanation of this phenomenon.

In a problem I have the following TeX code

Convert the permutation ( left(matrix{1&2&3&4&5&6&7cr $a[0] & $a[1] & $a[2] & $a[3] & $a[4] & $a[5] & $a[6]cr}right) ) $BR to standard cycle form (leave no spaces in your answer)

When I use jsMath it prints the intended two row matrix for the permutation. (enclosed by tall parentheses.)

When I use images it prints a single row with the fourteen items enclose by parentheses

Any explanation of why this happens would be greatly appreciated. Ken Appel kia@oregano.unh.edu

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$user$ John Jones - Re: TeX and Matrices $blueArrow$
11/19/2004; 5:36:30 PM (reads: 3587, responses: 0)

I am not familiar with \matrix as a LaTeX command. I guess it is a plain TeX command. Images for image mode are generated with LaTeX with a collection of macros added. Maybe there is a conflict there. How does it look in hardcopy?

John

PS It would be possible for others to try the code you posted via copy and paste if you use "pre" tags around it.

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$user$ Davide P. Cervone - Re: TeX and Matrices $blueArrow$
11/20/2004; 9:02:24 AM (reads: 3583, responses: 0)

Image mode calls LaTeX to process the mathematics, and it includes the amsmath package by default. It turns out that this package redefines \matrix and \pmatrix to generate errors (suggesting the use of the matrix and pmatrix LaTeX environments instead.) Image mode ignores errors in the TeX code, however, and so it keeps on trying to process the code. Since it has never entered the \halign that is part of \matrix, the & and \cr also produce errors (that are ignored), and the effect is that you get the numbers concatenated to each other as though there were nothing in between them.

There are several possible solutions. One would be to use \begin{array} and \end{array} rather than \matrix{}, as in

  \left(
     \begin{array}{ccccccc}
        1& 2& 3& 4& 5& 6& 7\\
        $a[0] & $a[1] & $a[2] & $a[3] & $a[4] & $a[5] & $a[6]\\
     \end{array}
  \right\)

Ideally you would use the pmatrix or matrix environments, but jsMath doesn't know about these; I'll have to add them in.

Alternatively, you can modify webwork2/lib/WeBWorK/Constants.pm to include

    {\catcode`\@=\catcode`\A
    \gdef\matrix@check#1%
        {\@xp\ifx\csname\@currenvir\endcsname#1\else\@@matrix@check@@#1\fi}
    \gdef\@@matrix@check@@#1\fi#2#3%
        {#2#3\csname end\expandafter\@gobble\string#1\endcsname}}

in $WeBWorK::PG::ImageGenerator::TexPreamble just before the \begin{document}. This disables the check for "old style" \pmatrix and \matrix commands and allows them to be processed normally.

Hope this helps.

Davide

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$user$ Kenneth Appel - Re: TeX and Matrices $blueArrow$
11/20/2004; 9:08:22 AM (reads: 3555, responses: 0)

Davide Thank you. I read John Jones message first and decided that my 20 year exclusive use of Knuth's book had to come to an end so looked for the comparable latex code, which is exactly what you supplied, and it worked perfectly Ken Appel

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$user$ John Jones - Re: TeX and Matrices $blueArrow$
11/20/2004; 10:00:45 AM (reads: 3543, responses: 0)

Hi again,

I should have also mentioned that webwork has commands for making matricies which should do the right thing in different modes. Since there are no answer boxes in this matrix, you could use

 ( display_matrix_math_mode([1,2,3,4,5,6,7], 
   [$a[0], $a[1], $a[2], $a[3], $a[4], $a[5], $a[6]] )

There are optional arguments to adjust the alignment of columns, or for the side delimiters. To use it, you need to load PGmatrixmacros.pl. For documentation run perldoc on PGmatrixmacros.pl.

John

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$user$ Michael Gage - Re: TeX and Matrices $blueArrow$
11/20/2004; 10:36:41 AM (reads: 3572, responses: 0)

Hi,

This is probably redundant at this point, but here is my summary of WeBWorK's behavior in displaying matrices.

DOCUMENT() ;

loadMacros(
PG.pl,
PGbasicmacros.pl,
PGchoicemacros.pl,
PGanswermacros.pl,
PGauxiliaryFunctions.pl,
PGdiffeqmacros.pl,
PGmatrixmacros.pl
) ;
############

TEXT(beginproblem());
@a = (0,1,2,3,4,5,6,7,8);

@b= (1,2,3,4,5,6,7,8, 9);

BEGIN_TEXT

Displays in jsMath but not in images mode (native TeX)
$PAR
( left(matrix{1&2&3&4&5&6&7\
$a[0] & $a[1] & $a[2] & $a[3] & $a[4] & $a[5] & $a[6]cr}right) )
$PAR
Displays in images mode but not in jsMath (LateX commands)
$PAR
( left(begin{matrix}1&2&3&4&5&6&7\
$a[0] & $a[1] & $a[2] & $a[3] & $a[4] & $a[5] & $a[6]crend{matrix}right) )
$PAR
Displays in both modes
(see http://webhost.math.rochester.edu/webworkdocs/docs/pglanguage/pod/pgmatrixmacros#display_matrix)
$PAR
{ display_matrix([~~@a,~~@b]) }

END_TEXT

ENDDOCUMENT();

Display in jsMath mode:

$jsMath_mode.png$

Display in image mode: $image_mode.png$

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$user$ Davide P. Cervone - Re: TeX and Matrices $blueArrow$
11/20/2004; 12:20:26 PM (reads: 3594, responses: 0)

I have updated jsMath to include the missing LaTeX environments for matrices. These include matrix, pmatrix, bmatrix, Bmatrix, vmatrix, and Vmatrix, which give matrices with no parens, round parens, brackets, curly braces, vertical bars, and double vertical bars, respectively. It has been updated in the CVS repository.

One caveat about the display_matrix command: the entries are not automatically in math mode, so if you look carefully at Mike's examples above, you'll see the numbers look different in the lower three matrices from the two above them. That's not a complaint, just a detail to be aware of. (I'm sure that it is set up that way so that you can have answer rules within the matrices generated by display_matrix; they are not allowed in math mode.)

Davide

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$user$ Arnold K. Pizer - Re: TeX and Matrices $blueArrow$
11/22/2004; 10:43:41 AM (reads: 3577, responses: 0)

Let me add an additional comment on Davide's caveat. Davide is definitely correct that with display_matrix the entires are not automatically put in math mode. The reason is, as Davide surmises, that with display_matrix you can put in answer rules and also math [using e.g. $ sin(x) $]. If all your entries are mathematical expressions, you should use display_matrix_math_mode (or the equivalent display_matrix_mm) as in John Jones' example above.

Arnie

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$user$ John Jones - Re: TeX and Matrices $blueArrow$
11/22/2004; 12:27:35 PM (reads: 3546, responses: 0)

Hi,

When I mentioned display_matrix_mm, I was going on what I expected that it did, and not so much on what it really does (it has been a long time since I looked at it). At the moment, I can't make it do anything useful for matricies with formulas in it (or any bits of math mode in it). On the other hand, display_matrix was working correctly (where you have to explicity put entries in math mode as described above, e.g., '$ \sin x$').

Maybe I should change it so that it does not mbox its entries? Then it will work more as expected. Since it is hard to make it handle formulas now, presumably this won't break existing problems?

John

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Kenneth Appel - TeX and Matrices

Kenneth Appel - TeX and Matrices