Syntax bug with PGlateximage.pl and negative parameter values about pg

[drgrice1]

This is technically not a bug, but an unimplemented feature. There is no special handling for passing a MathObject to TikZ in this manner. What is happening is that the MathObject formula is interpolated into the string via MathObject stringification. That will most likely cause problems in quite a few scenarios as MathObject stringification isn't designed to produce what the pgfplots package needs.

[Alex-Jordan]

Glenn is right and in general we want to be aware of things like brackets and any other thing that could be in MathObjects string output that is not good for whatever latex image-making tool is being used. The feature to use tikz in WeBWorK problems did not come with a promise that \addplot {$f}; would always work.

One thing you can do is Context()->flags->set(showExtraParens => 0);. This will reduce instances of nested grouping symbols. In your case, it leads to 0.1*(x--1)*(x--2)*(x-4) which pgfplots has no problem with.

In this particular case, you can also use reduce like:

$f=Formula("$a*(x-$r)*(x-$s)*(x-$t)")->reduce;

leading to 0.1*(x+1)*(x+2)*(x-4) which is of course also good.

[sean-fitzpatrick]

Thanks. I guess this became less of a bug report and more of a feature request. But simply reducing first would help here (and is probably good practice in any case).

Other pitfalls will likely require manual entry of functions into TikZ: e.g. domain for trig functions needs to be converted to degrees.