Hi Stuart,
Wouldn't taking the absolute value of the expression inside the sqrt function
also work? I tried this, thinking it would remove the negative number problem,
but it did not work:
$fnct_rms_halfwave="1/sqrt(pi) * sqrt( abs(1/2*(pi-x*pi/180) +
1/4*sin(2*x*pi/180)) )";
I checked my gnuplot manual, and abs() appears to be the correct syntax for
absolute value. Wouldn't that fix the negative number issue?
These are the lines IT sent me from the error log:
[Mon Apr 06 10:59:07 2020] [error] [client 128.210.56.177]
"/home/httpd/perl/tmp/glhardin_purdue_1586185147_62400672_plot.data", line 13:
expecting ':', referer:
https://loncapa.purdue.edu/priv/purdue/ecet_purdue/Topics/Power_Electronics/Thyristors/Calc_FiringAngle_using_Graphs_GeogebraInteractive_Multipart.problem
[Mon Apr 06 11:17:06 2020] [error] [client 128.210.56.177]
"/home/httpd/perl/tmp/glhardin_purdue_1586186225_6003521_plot.data", line 13:
expecting ':', referer:
https://loncapa.purdue.edu/priv/purdue/ecet_purdue/Topics/Power_Electronics/Thyristors/Calc_FiringAngle_using_Graphs_GeogebraInteractive_Multipart.problem
[Mon Apr 06 11:18:32 2020] [error] [client 128.210.56.177]
"/home/httpd/perl/tmp/glhardin_purdue_1586186312_6039374_plot.data", line 13:
expecting ':', referer:
https://loncapa.purdue.edu/priv/purdue/ecet_purdue/Topics/Power_Electronics/Thyristors/Calc_FiringAngle_using_Graphs_GeogebraInteractive_Multipart.problem
[Mon Apr 06 14:42:22 2020] [error] [client 128.210.56.177]
"/home/httpd/perl/tmp/glhardin_purdue_1586198542_65331252_plot.data", line 13:
expecting ':', referer:
https://loncapa.purdue.edu/priv/purdue/ecet_purdue/Topics/Power_Electronics/Thyristors/Calc_FiringAngle_using_Graphs_GeogebraInteractive_Multipart.problem
Do they make sense to you? Line 13 in the LON-CAPA code is part of a
<startouttext /> statement, so I don't think that's the line the errors are
referring to. I looked through the code again, and do not know where it might
be expecting to see a ":" character, although I have done many versions of this
during troubleshooting, and I wonder if this error came from a version when I
was using the ternary operator to limit the plot interval.
Gene L. Harding, PE
Associate Professor of ECET
Purdue University
574-520-4190
https://polytechnic.purdue.edu/south-bend/
-----Original Message-----
From: LON-CAPA-users <[email protected]> On Behalf Of
[email protected]
Sent: Tuesday, April 7, 2020 8:50 AM
To: Discussion list for LON-CAPA users <[email protected]>
Subject: Re: [LON-CAPA-users] gnuplot problem
Gene,
>
> Two of them work fine, and the other two, which both have sine
> expressions inside a sqrt function, do not.
>
My guess would be that gnuplot is encountering an issue because floating point
arithmetic results in evaluation of the square root of a negative number (very
close to zero), which should really be 0.
In that case an alternative would be to explicitly evaluate the components of
the function within a perl script block in LON-CAPA, and test that they will
not result in a negative number before applying LON-CAPA's sqrt() function to
the result (rom which you would then add the value to an array (@Y) of y values
for the plot). The array (@X) will contain the corresponding x values, which
you would have generating within the loop you use to generate the y values (in
the @Y) array.
You would then replace use of the <function></function> tag with
<data>@X</data>
<data>@Y</data>
where @X and @Y are arrays containing x and y values for the points on the plot.
See the: "Data Plot with Numerical Response" example in the problem templates.
Stuart Raeburn
LON-CAPA Academic Consortium
________________________________________
From: LON-CAPA-users <[email protected]> on behalf of
Harding, Gene L <[email protected]>
Sent: Monday, April 6, 2020 7:35 PM
To: Discussion list for LON-CAPA users
Subject: Re: [LON-CAPA-users] gnuplot problem
Thanks Stuart. I do not have access to those directories (as far as I can
tell), so have reached out to some IT folks to see if they can help me. I
realized later that, apparently, "dynamically generated plot" is just the alt
tag for the gnuplot.
I am baffled about what is going on. I have four functions for this problem.
Two of them work fine, and the other two, which both have sine expressions
inside a sqrt function, do not. I have tried using the ternary operator to zero
out values outside of the axis limits. In all of the playing/troubleshooting I
have done, it appears to not like the sqrt(bla bla sin(stuff)). I am not sure
what version of gnuplot we are using.
I think I am just going to do the problem using Geogebra and forget about
gnuplot, but it would be nice to know what's going on with the gnuplot.
Hopefully, my IT guys can help...
BR,
Gene L. Harding, PE
Associate Professor of ECET
Purdue University
574-520-4190
https://urldefense.com/v3/__https://polytechnic.purdue.edu/south-bend/__;!!HXCxUKc!jTjoyEwsimPmL2daj4jh1wXvO-ThMXDm58g_FiI6994pTe0-lVckSwwcNawAEA$
-----Original Message-----
From: LON-CAPA-users <[email protected]> On Behalf Of
Raeburn, Stuart
Sent: Monday, April 6, 2020 3:11 PM
To: Discussion list for LON-CAPA users <[email protected]>
Subject: Re: [LON-CAPA-users] gnuplot problem
Hello Gene,
If the text: "dynamically generated plot" is displayed instead of an image,
when using gnuplot, then it means gnuplot was unable to process the data file
generated by LON-CAPA for your plot.
That data file will have been written to /home/httpd/perl/tmp/ on your server's
filesystem with a file name that includes your username, and ends _plot.data.
and there will also be an error message in the web server's error log file,
e.g., /var/log/httpd/ssl_error_log, with your problem listed as the referer.
(You'd need to ask your system administrator to look in the log files).
I was able to successfully generate plots for both functions:
$fnct_rms_halfwave="1/$pi * &sqrt(1/2*($pi-x) + 1/4*sin(2*x))";
$fnct_rms_fullwave="&sqrt(2/$pi) * &sqrt(1/2*($pi-x) + 1/4*sin(2*x))";
in a problem in my Authoring Space (gnuplot version: 4.4.2).
You might double check that there is not a typo in the problem XML, where you
refer to the function, e.g., <function>$fnct_rms_halfwave</function>
Otherwise, there could be an issue with other attributes defined for the plot,
aside from the functions themselves (although in most cases, LON-CAPA replaces
invalid values with valid ones, before creating the _plot.data file passed to
gnuplot).
Stuart Raeburn
LON-CAPA Academic Consortium
________________________________________
From: LON-CAPA-users <[email protected]> on behalf of
Harding, Gene L <[email protected]>
Sent: Monday, April 6, 2020 11:22 AM
To: Discussion list for LON-CAPA users
Subject: [LON-CAPA-users] gnuplot problem
Hi everyone,
I am having trouble generating a gnuplot using the following two functions in
LON-CAPA:
$fnct_rms_halfwave="1/$pi * &sqrt(1/2*($pi-x) + 1/4*sin(2*x))";
$fnct_rms_fullwave="&sqrt(2/$pi) * &sqrt(1/2*($pi-x) + 1/4*sin(2*x))";
Instead of rendering a plot, LON-CAPA just displays a message that says
"dynamically generated plot". It plots fine in Geogebra. Does anyone know
what's going on with the gnuplot?
Best regards,
Gene L. Harding, PE
Associate Professor of ECET
Purdue University
574-520-4190
https://urldefense.com/v3/__https://polytechnic.purdue.edu/south-bend/__;!!HXCxUKc!jTjoyEwsimPmL2daj4jh1wXvO-ThMXDm58g_FiI6994pTe0-lVckSwwcNawAEA$
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