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Arnold K. Pizer - Trouble with latex2html - bad images

Arnold K. Pizer - Trouble with latex2html - bad images

by Arnold Pizer -
Number of replies: 0
inactiveTopicTrouble with latex2html - bad images topic started 2/10/2001; 12:02:34 PM
last post 2/10/2001; 12:02:34 PM
userArnold K. Pizer - Trouble with latex2html - bad images  blueArrow
2/10/2001; 12:02:34 PM (reads: 1211, responses: 0)
Typeset mode uses latex2html which is a very slow process and is also subject to random errors which may cause a student's problem to be unviewable in typeset mode. Depending on the speed of your server and the complexity of the problem, it may take 6 seconds per student per problem to create the problem the first time it is created. For this reason we cache the problem images in typeset mode (and suggest you precreate them) which speeds things up tremendously but can cause other complications. What follows is a pretty detailed explaination of what is going on and some suggestions regarding the use of typeset mode.

If a student can not view a problem, tell them to switch to "formatted text" mode and they will be able to view the problem (they can also use the hard copy). Here is how things work and how to fix them so the student can use typeset mode.

When a student views a problem in typeset mode, webwork looks for a directory where the images should be (I'll tell you where below). If the directory exists and is more recent then the date of the problem .pg file, webwork uses the images in that directory. Otherwise it (re)creates the directory. Thus if somehow bad images are created, that is all a student will see. To fix this, you just have to remove the bad directory. These directories are under l2h in the tmp directory. By default this is e.g.


but we suggest you put this in a separate file system e.g /home/htdocs/tmp and then you would have /home/htdocs/tmp/mth161/l2h

under l2h/ you will see e.g

drwxrwx---      4 wwhttpd  MTH161     512 Dec 13 21:56 1-40080/
drwxrwx--- 113 wwhttpd MTH161 3072 Dec 16 12:44 set0/
drwxrwx--- 1102 wwhttpd MTH161 21504 Dec 16 14:00 set1/
drwxrwx--- 4153 wwhttpd MTH161 75264 Dec 15 15:15 set10/
drwxrwx--- 5079 wwhttpd MTH161 93696 Dec 16 15:08 set11/
drwxrwx--- 1879 wwhttpd MTH161 41984 Dec 16 13:55 set12/
drwxrwx--- 4127 wwhttpd MTH161 88064 Dec 15 14:51 set13/
drwxrwx--- 4122 apizer MTH161 87552 Dec 15 17:13 set14/
drwxrwx--- 1851 apizer MTH161 40960 Dec 16 05:17 set15/
drwxrwx--- 7048 apizer MTH161 134144 Dec 22 20:05 set2/
drwxrwx--- 5579 wwhttpd MTH161 104448 Nov 22 15:19 set3/
All you should see are set0, set1, etc. The 1-40080/ is a bad directory.

Under a set you will set e.g. .../l2h/set2/3-45678

This is the directory for prob 3 from set2 for psvn number 45678. If the student with psvn 45678 had trouble viewing prob 3 in set2, this is the directory your would remove. The directories are created under l2h and then at the last stage moved under the proper set so if they don't get moved, they are bad which is what happened in the case of the directory 1-40080/ above.

If you remove a student's directory you can check that things are OK by viewing the student's problem. From the prof page (item 3) go to this student's entry and view the problem in typeset mode. This will run latex2html and rebuild the typeset html page.

Even if the directory gets moved to the proper location (e.g. under .../l2h/set2/), there may be bad images. Bad images seem to be a random problem which is related to the speed and load on your server. If you have a fast server, you will almost never see this problem. If you have a slow heavily loaded server, you will see it a lot. Preceateing the latex2html images is a very good way to avoid this problem. Otherwise at busy times many students may be viewing problems for the first time which causes latex2html to be called which puts a high load on the server which makes these random errors more likely.

How can you recognize when and where these random errors have occured (other than receiving an email from a student)? If a directory e.g. set2/3-12345/ contains any files of the type *.old or *.css or a subdirectory named l2h*, it is bad and should be removed. Maybe we should write a script which searches for and removes such directories, but we haven't found that necessary.

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