Airport Express

I saw a blurb (it must be several years ago) about using an Apple wireless device called Airport Express to play music files from my computer over a WiFi network on remote speakers. I bought an AE recently, plus a miniature amplifier from Amphony and some bookshelf speakers from Polk Audio through Newegg.

I was surprised, and quite disappointed, to find that in order to use this device in the normal way one must be a member of the "Apple club." That is to say, in order to send audio from my computer to Airport Express and have it come out through speakers, I need to have an Apple ID so that I can do "Home Sharing." I think this is outrageous. However, I do think it was pretty cool, in the end, to control this setup with my iPhone running an App called Remote.

I've never owned a non-Apple computer. That's a lot of boxes, starting from 1984. And I love OS X and its integration of the pretty Mac side with Unix underneath. However, it's clear that the future is iOS, i.e. not folks like me. So I was pleased to find, in a quick Google search, a somewhat dated article which explains how to stream audio in this way with Linux hardware.

About the amp, it is fun to produce music with so little hardware on site, but there is no ON/OFF switch for output, though there is a dial, which when dialed down still sends a nasty signal through the speakers when powering down. And I do like the sound a lot. Nice speakers!

Go Snail Go

I came across a post which solves what it calls the "snail" problem in Go. We've seen some very pretty examples of the same thing in Python here.

This is the output of my version in Go for S = 9.

1  2  3  4  5  6  7  8  9 32 33 34 35 36 37 38 39 10 31 56 57 58 59 60 61 40 11 30 55 72 73 74 75 62 41 12 29 54 71 80 81 76 63 42 13 28 53 70 79 78 77 64 43 14 27 52 69 68 67 66 65 44 15 26 51 50 49 48 47 46 45 16 25 24 23 22 21 20 19 18 17

You can see why he called it the snail. Anyway, I noticed a chance to use a goroutine for this problem. In any cycle starting with [left] followed by [down] we go n steps in each direction, then n+1 steps in the [right,up] directions. In the code below, we obtain these step values from a Go channel.

A couple of other Go-like things about this code. We stash the 2D array (as a 1D array with a shape parameter) in a struct, and then attach a func to that struct to pretty print it. The details of the pprint function could doubtless be improved---I'm not too swift with formatting. The other Goish thing is to modify both the row and column indices at once, returning what we'd call in Python a tuple value from the step function.

Fun.

package main import ( "fmt" "os" "strings" ) func dist(ch chan int) { var a int = 1 for { ch <- a ch <-a a++ } } var m = map[string]string{"L":"D","D":"R","R":"U","U":"L"} func step(r, c int, dir string)(rn, cn int) { switch dir { case "L": { c-- } case "D": { r++ } case "R": { c++ } case "U": { r-- } } return r,c } type A struct { arr []int; SZ int } func (a *A) pprint() { d := a.SZ for i:= 0; i < len(a.arr); i += d { S := []string{} for _,f := range a.arr[i:i+d] { S = append(S,fmt.Sprintf("%2d", f)) } fmt.Println(strings.Join(S," ")) } } func main() { S := 9 if S%2 != 1 { os.Exit(1) } N := S*S a := A{make([]int,N), S} ch := make(chan int) go dist(ch) dir := "L" var r, c int; r = S/2 + 1; c = r n := <- ch for { for i := 0; i < n; i++ { //fmt.Println(r, c, N) a.arr[(r-1)*S + (c-1)] = N N-- if N == 0 { break } r,c = step(r, c, dir) } n = <- ch dir = m[dir] if N == 0 { break } } a.pprint() }

Go, again

This is a brief, updated report on my exploration of the Go language. (First post here). For an idea about what Go can do I encourage you to check out another video with Rob Pike (and Russ Cox). Not to disrespect Russ, but as a great example, check out the segment starting about 21:25. It's amazing.

The source of that program is here.

In order to play with this stuff, you will have to download the compiler source and build it. I assume you can do that, if not, drop me a line.

I've spent a total of about 40 hours on Go over the last week, and I can say that I believe this is all quite correct:

The Go programming language is an open source project to make programmers more productive. Go is expressive, concise, clean, and efficient. Its concurrency mechanisms make it easy to write programs that get the most out of multicore and networked machines, while its novel type system enables flexible and modular program construction. Go compiles quickly to machine code yet has the convenience of garbage collection and the power of run-time reflection. It’s a fast, statically typed, compiled language that feels like a dynamically typed, interpreted language.

The more I explore, the better I like it. Go does "feel like a dynamically typed, interpreted language." Exactly. And using TextMate I can just do CMD-R and the build, linking and execution happen painlessly.

I wrote about 30 or so short programs to explore simple tasks in Go. I also wrote two different versions of the PSSM code discussed here, and in subsequent posts. And I played with Bruce Eckel's code from here. A zipped folder of all this stuff is on Dropbox. It's not very well documented but only the intrepid will follow this lead anyway.

I'm hooked. I have a lot of work to do figuring out the interface and concurrency stuff. And it is great fun!

Go fib

I've been having fun with a new programming language called Go, developed by Rob Pike and friends at Google (video). Somehow I missed hearing about it until now. I'm not leaving my true love, Python, but there's a lot to like about Go as a replacement for C and C++.

Go has

garbage collection, so there are no worries about managing memory

no classes, but simply attaches methods to types

a simple syntax compared to C---eliminating most semicolons

much less complexity than C++

goroutines to launch parallel processes that communicate using channels

maps and string support, and slices as a kind of resizable array

multiple return values from a function

combined var declaration and assignment with type of rhs

pointers but no pointer arithmetic

the ability to construct and return a local variable from a function.

great docs, is compiled, and fast.

Go has interfaces, which I don't understand very well, but they can be used to give polymorphic behavior.

Here is a simple, familiar Go program using a goroutine and a channel. Notice that the type declaration comes after the variable name, and the arrow symbol for flow into and out of the channel, c.

package main import "fmt" func fib(c chan int) { var a, b int = 1, 0 for { c <- a a, b = a + b, a } } func main() { c := make(chan int) go fib(c) for i := 1; i < 12; i++ { f := <- c fmt.Println(f) } }

fib() will generate values as long as we want, similar to a Python generator. Output:

1 1 2 3 5 8 13 21 34 55 89

I found a Go "bundle" for TextMate here.

Fee, fi, foe, fum

I found myself wondering about the correct pronunciation of the Greek letter φ (phi). Somehow, I acquired the habit of saying "fee." But it turns out that mathematicians say "fi" as in "fly."

It seems that in Greek, the first pronunciation is correct. However, if we were to follow that route, we'd have to pronounce π as "pee," and that just feels wrong.

A more common question is about "data." See howjsay. I pronounce data like "date-uh." I have a memory of this being drummed into me in Latin class. Perhaps we should just "say it like the Romans did," but see the above for one problem with that approach. Anyone know an authoritative source?

One year, one world

Yesterday was the one-year anniversary of the flag counter widget. We have 144 countries, including a new one: Cote D'Ivoire. It makes me very happy to see all these ≈25K (unique) visitors, even if I don't know that much about them.

From Google's stats, it looks like most people are interested in maybe 25-30 pages. I think there is more good stuff buried here, so perhaps I'll make a post about my favorites one of these days. What I'd love to see, is data that showed a person arriving and then poking around for a while. Sometimes you see a hint of this, but the stats really don't tell that much.

Anyway, thanks for reading! And don't forget to check out the Python book.

And, I'm still waiting for Tonga.

R.W. Hamming

I received a new book in the mail today. I'm a huge fan of Richard Hamming (e.g. this), and the book is everything I hoped for.

I thought I would just post a quote (from him, not one of the many interesting quotes he includes):

The taste to work on the right problem at the right time and in the right way is the secret of doing significant things.

To focus on just one aspect: what you are trying to do must be doable. Timing is (almost) everything.