CSC151.01 2014F, Class 40: Vectors ================================== _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * Reading check. * Behind the scenes: How Scheme implements vectors. * Lab. Preliminaries ------------- ### Admin * New partners (some cards may be missing, so we'll adapt)! * Review sessions * Tonight at 8pm with Alex * Tomorrow at 8pm with Ajuna * Tomorrow at 10am with SamR ### Upcoming Work * Lab writeup: Exercise 5, * Readings for Friday: * [Randomized Drawing](../readings/random-drawing-reading.html) * *Required* exam epilogue due tonight. * Part one of the project due next Monday night. * Sketches due in class on Tuesday. * Study for quiz! ### Extra Credit Opportunities #### Academic * Scholars' Convocation, noon, today: Dean Latham. * Town Hall Thursday on Sustainability, noon and 7:30 p.m. (I think) * CS Table Friday: Shellshock #### Peer Support * Football, Saturday at noon vs. Lawrence. * YGB, Saturday at 7:30, See, Bring, Lou, Us * Karan's radio show 11pm Thursday nights on KDIC * Evan's radio show 5pm Friday nights on KDIC * Donna's radio show Sunday midnight on KDIC ### Questions _How do I do other cool things with GIMP/gigls?_ > There's a huge list of procedures under Help -> Procedure Browser. You can call most of them, although the arguments are a bit strange in some cases. Reading check ------------- With your partner: * Most important points of the reading * Confusing issues Most important points _Why do vectors in addition to lists?_ > Sometimes we want quick access to values; lists are slow, vectors are fast (by index). > Vectors let you change their contents. _Why have lists if we have vectors?_ > Lists can be expanded easily; vectors can't. > Lists are really easy to recurse over. _Huge number of procedures_ Confusing issues _Why would you ever want `vector-fill!` (particularly given that we could just use make-vector)?_ > Mostly there to help you think about recursion over vectors. _How do we make vectors bigger?_ > You can't. _What's a number vector?_ > A vector that contains only number. Behind the scenes: How Scheme implements vectors ------------------------------------------------ Laid out in a continuous area of memory. Let's say it starts at location *m*. Every value takes the same amount of space, *s*. That means that value *i* is at position *m*+*si*. Lab --- * Why do we have `vector-fill?` answered: We can't redefine things. Hence, if we want to change them, changing in place is the way to go. * Two approaches to `vector-sum`, just like there are two approaches to the normal `sum`. You can use direct recursion or you can use a helper. * I like that many of you are finding a similar procedure and then just changing the appropriate parts.