Practice meeting, Jan. 21st

[Lyle Kopnicky]

When: Jan. 21st, 6:30-8:30pm

Where: Collective Agency Downtown, Suite 1108, 511 SW 10th Ave, Portland, OR (opposite side of the floor from the elevators)

We'll begin discussing Chapter 5, "Data Parallel Programming with Repa", of Parallel and Concurrent Programming in Haskell. At the meeting anyone will be able to present and contribute to the discussion.

Meetup link to RSVP:

https://www.meetup.com/Portland-Functional-Programming-Study-Group/events/qjbbjqyzcbcc/

Hope to see you then!

[karoyakani]

In the "Example: Image Rotation" I failed to install the "repa-devil" package.

In stead I used Data.Array.Repa.IO.BMP.

See code : https://gist.github.com/karoyakani/d526bc778e0296ad75feb6751b061502

Test BMP file : http://entropymine.com/jason/bmpsuite/g/rgb24.bmp

- TJ

[Lyle Kopnicky]

Thanks. Yeah, I was having trouble figuring out how to install repa-devil too. There are version conflicts.

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[Lyle Kopnicky]

I was able to get repa-devil to build by using an old stack resolver version (which installs an older GHC). I modified the stack.yaml file as follows:

https://gist.github.com/lylek/41eab0d7e9c0f0ab1029da084d76a141

Then I was able to build the program with:

stack build --flag parconc-examples:devil parconc-examples:exe:rotateimage

and run it with:

stack exec rotate image 4 wonky.jpg straight.jpg

I also had to install the DevIL library on my system. On my Mac I did this with:

brew install devil

[Lyle Kopnicky]

In the meeting, we tried to get the rotateimage program to produce a transparent alpha channel. I changed the data constructor from RGB to RGBA in the program. That didn’t work - it yielded a run-time pattern match failure.

I managed to get it to work now. When I converted the jpg to png, I had to add an alpha channel. The command (using ImageMagick) is:

convert -alpha set wonky.jpg wonky.png

That gives it an alpha channel, that is set at every pixel. Then when I run the modified rotateimage program on it, it rotates it and leave the unfilled area as transparent, instead of black.

- Lyle

[Lyle Kopnicky]

I was also having trouble installing llvm 3.5 in the meeting, which is the version needed for compatibility with the older version of GHC I’m using.

Well, that turned out to be simple. I just downloaded the binaries from http://releases.llvm.org/download.html#3.5.0, and put them in my PATH.

But after compiling with the llvm flag, the programs don’t seem to run any faster.

- Lyle

[Lyle Kopnicky]

Correction: I think I was doing something wrong trying to build with llvm using “stack build”. When I built using “stack ghc” I was able to get it to use llvm.

So now I can give better figures for comparison.

fwdense 500 runs in 2.5 seconds without -fllvm, under 1.5 seconds with -fllvm

fwdense1 500 with 2 threads runs in 1.9 seconds without -fllvm, 1.3 seconds with -fllvm