--- a/README.markdown Sat Feb 22 23:03:43 2020 -0500
+++ b/README.markdown Sun Feb 23 13:41:09 2020 -0500
@@ -875,3 +875,42 @@
Started reading one of Tufte's books. Found a beautiful graph from a 1979 paper
(`10.1126/science.206.4421.987`) with a gorgeous plotter font. Need to try to
find a similar font to use myself.
+
+## 2020-02-23
+
+Did another graphing exercise from Campbell Biology in gnuplot for fun.
+
+Figured out that `dashtype ''` in my style files was causing the *line* to show
+as solid, but the entry in the key was blank! Turns out `dashtype solid` is
+what I actually want. Also learned that I need to explicitly reset that when
+I want a solid line, otherwise the dashtypes I set in previous styles will carry
+over.
+
+Refined my color plotting style to use dashed lines instead of lighter colors
+for types 6-10. Seems easier to read that way — the light colors were *really*
+light.
+
+Figured out how to do linear regression in gnuplot, and made some helper
+functions to make it less annoying:
+
+ # lr = linear regression (the function to fit)
+ # lrt = linear regression title
+
+ baselrt(mm, bb, mprecision, bprecision) = sprintf(\
+ sprintf("%%.%dfx + %%.%df", mprecision, bprecision), \
+ mm, bb)
+
+ lr(x) = m * x + b
+ lrt(mp, bp) = baselrt(m, b, mp, bp)
+
+ lr2(x) = m2 * x + b2
+ lrt2(mp, bp) = baselrt(m2, b2, mp, bp)
+
+ fit lr(x) "plant-co2" using "CO2":"Corn" via m, b
+ fit lr2(x) "plant-co2" using "CO2":"Velvetleaf" via m2, b2
+
+ plot [300:1050] \
+ "plant-co2" u "CO2":"Corn" w lp, \
+ "plant-co2" u "CO2":"Velvetleaf" w lp, \
+ lr(x) t lrt(3,0) lt 6, \
+ lr2(x) t lrt2(3, 0) lt 7