SUNY Geneseo Department of Mathematics

Files

Friday, April 28

Math 230 02
Spring 2017
Prof. Doug Baldwin

Misc

Online Course Survey

The Provost’s Technology Advisory Committee is interested in students’ experiences with online courses, whether as a taker of them or as a non-taker, and whether from Geneseo or other schools. You’re likely to get a request to fill out a survey on this subject. Please do so if you get the request.

Final Exam

Monday, May 8, 8:00 AM.

Comprehensive, but emphasizing material since second hour exam (e.g., vectorization, strings, cell arrays, etc.).

Designed for around 1 1/2 hours, you’ll have 2 1/2.

There may be one closed-book question, but the rest will be open-references and open-computer (but closed-person) as in the past.

Rules and format otherwise similar to hour exams, especially open-references rule.

Sample exam in “Final Materials” folder under “Files” in Canvas.

I’ll bring donuts and cider.

SOFIs

5 (!) responses as of last night.

Questions?

Loading and Saving Files

Section 4.12

Concepts

What’s the point? Why would you want to load or save files? Mainly in order to save “state” (i.e., values of variables) that needs to be used in another Matlab session but that takes a long time to build up. It’s better to save this state the first time you create it and restore it when you need it later than to have to rebuild it every time you need it.

What did the reading have to say about doing it?

The save( 'filename' ) function saves the workspace.
- The file you save in needn’t already exist; Matlab will create it, with a “.mat” extension, if necessary.
load( 'filename' ) reads data back from a file, which must already exist and have a “.mat” extension
Matlab has “wizards” to “interactively” import data. What does this mean?
- If you want to import data from other programs, maybe spreadsheet or database programs, Matlab can walk you through the process.
- Or, in some cases, Matlab has built-in functions that will do the whole process automatically, e.g., we found readtable to import an Excel spreadsheet.
Saved variables are in “binary” format rather than something else (maybe text?)
- Conside all the different ways you might represent a number: as a string of digits (e.g., 17), in Roman numerals (e.g., XVII), etc.
- Computers use a binary (base 2) representation that is closely tied to the electrical signals on which computers really work. For example, the number 17 might look to a computer like 00000000000000000000000000010001. This, rather than a more human-readable form, is what is saved in a “.mat” file.

Practice (Plus Practice with Cell Arrays)

There’s a Matlab function that “plays” a game of Mad Libs, and two sample Mad Libs, in the “Lab Files” folder of our “Files” area in Canvas. In particular...

play2.m is the “player” function.
fairytale.mat is a Mad Lib of a fairy tale.
instructions.mat is a Mad Lib of a set of instructions for doing something.

Download these files to your computer.

Looking at the comments in play2.m, figure out how a Mad Lib is represented.

Cells play a part
So do strings
... but just what is this “representation” idea?

Matlab has built-in types for things like numbers, matrices, cell arrays, strings, etc. But most large programs involve things that conceptually are not any of the built-in Matlab types. For example, there is no “Mad Lib” or “Eliza dialog” type, yet you are working with programs that deal with those things. “Representation” is about figuring out how to use Matlab types to capture the more abstract things a program “really” works on.