Thanks for the reply Alexey.
I got it to work; the Google AI engine is very helpful. I attached the two source files, sinewave.cc and sinewave.tcl. I used FreeBSD to build with command
c++ -g -I/usr/local/include -I/usr/local/include/tcl8.6 -I/usr/local/include/tk8.6 -L/usr/local/lib -lGL -ltcl86 -ltk86 -lmgl2 sinewave.cc -o sinewave
You can click on the Demo 1 button to show the plot; I attached the resulting window. The display was sent to a 13,3 in MacBook with a 2560x1600 resolution.
Would you have a suggestion how I can improve the quality of the text in the plot?
Thanks again,
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DL