Notes after discussion of Chapters 1-2, Jan. 13-15, 2014

Monday: Syllabus, what is informatics, entry survey.

Wednesday: discussion based on students’ notes for ch. 1-2; “lab” on survey.

Very good discussion!

1. A student asked: How are algorithms different from programs? Textbook: programs are specialized to particular conditions or assumptions and are usually written in a programming language.

• Reference to programming language seems circular. It is a language which the computer can execute, completely precise and unambiguous. Specialization to particular conditions doesn’t seem important. Main point: a program is the expression of an algorithm in a language the computer can execute. Also mentioned: programs can combine multiple algorithms.

2. We enacted the letter search algorithm using English character frequency and a five-letter word, with one student as author, one as assistant, and one counting the letters the assistant had to point at. 43 pointings for the word TUBES (or maybe TUBED).

3. One student asked: Why 0’s and 1’s? Does it speed things up? I can copy letters accurately [even though there are more than 2 letters].

• We revisited the letter search algorithm using binary representations of letters. We discovered we would need 5 bits for a 26-letter alphabet. The student noted that we could take a short cut: if the letter sequence is 0, 1, if the author blinks on 0, it’s 0, and if not, it’s 1, so no need to point at 1. (Could also be used to skip last of 26 letters, if the author doesn’t blink on the first 25.) Taking this approach, the assistant had to point at 25 letters for TUBES, because there are 5 letters and each requires 5 bits and one pointing per bit was sufficient using the “blink or not blink” shortcut.

(We also noted that 1 bit gives us 2 values, 2 bits 4 values, 3 bits 8 values, and in general adding one bit doubles the number of values that can be represented.)

• But in general, binary wasn’t selected because it makes things go faster, but because the arithmetic circuitry is less complex (4 addition facts instead of 100) and therefore less costly.

• Also pointed out the ability to copy “without errors” depends on there being an uninhabited gap between the voltage ranges for 0 and for 1; if the ranges touched, there would be many errors in the border region.

Lab: Discussion of some points on the entry survey.

• Checking the solutions found for learning how to do something in a text/word document.

• How to cite a web page (author, title, URL, date retrieved).