plplot-tcl binary package in Ubuntu Bionic i386

 PLplot is relatively small, portable, freely distributable, and is rich
 enough to satisfy most users. It has a wide range of plot types including
 line (linear, log), contour, 3D, fill, and almost 1000 characters
 (including Greek and mathematical) in its extended font set. The package
 is designed to make it easy to quickly get graphical output; only a
 handful of function calls is typically required. For more advanced use,
 virtually all aspects of plotting are configurable.
 .
 This package contains the Tcl/Tk support for PLplot: shared libraries,
 Tcl modules and the Tk driver.

Source package