GROWBY 20% 10 [FD 20 RT 90]
Part I: There are two commands that make create repeating
patterns that change size. The GROWBY command and the GROWGBY
command. The command: GROWBY changes the lengths evenly while
the GROWGBY command them geometrically. For example GROWBY 20%
10 [FD 20 RT 90] will create a spiral with lines of length:
20,24,28,32,36 etc.
while GROWGBY 20% 10 [FD 20 RT 90] will make
lines of lengths 20,24,24*1.2=28.8,28.8*1.2=34.56 etc. Each
line will be 20% longer than the previous one.
GROWBY 20% 10 [FD 20 RT 90]
GROWGBY 20% 10 [FD 20 RT 90]
Thus to generate the sequence of lengths 10,15,20,25,30... one
needs to use the GROWBY command with the growth rate of 50% since 15
is 50% more than 10. In the same way the sequence
20,22,24,26,28 will be generated by the command
GROWBY 10% 5
[something] (where something define the "seed" of the
picture. If the letter G is inserted to indicate the
geometrical growth then the first sequence (GROWGBY 50% 4
[something]) will become 10,15,22.5,22.5*1.5,etc. and the
second sequence 20,22,22*1.1,22*1.1*1.1,etc.
Sometimes the growth rate could be negative. For example the command GROWBY -10% 8 [CIRCLE 80] generates circles of radii 80,72,64,56... while GROWBY -10% 8 [CIRCLE 80] will make the sequence geometric: 80,72,72*0.9,72*0.9*0.9,etc.
Test your understanding of these commands by changing the red
pictures into black in the exercises:
Paper
self test: