On Fri, Nov 18, 2011 at 12:49:55PM -0500, Raul Miller wrote:
> I think that representative data, along with a description of the result
> and purpose of the code would work. (Or, if not, that should be enough for
> us to ask intelligent questions.)
I've been disinclined to share the problem because it is intended to
be used to help our organization make hiring decisions, as a kind of
one-up FizzBuzz. It's inspired by this Mars Rover problem:
http://thefundoowriter.wordpress.com/2009/10/01/the-mars-rover-problem/
Anyway, I'm going to break the code of silence because I figure
solutions in J are unlikely to be helpful to applicants where I work,
since they have to code in Java anyway.
The task is to simulate antenna motion for scans here at the VLA. We
choose a very simplistic and unrealistic simulation. I have an input
file that looks like this:
V 124.7 39.9 5
C 125.9 40.8 3.5
T 127.1 41.6 1.3
C 128.4 42.4 3.5
This is a list of scans. The leading character is one of three values,
C, T, and V representing Calibration, Target and Variable-length
scans. The second and third values are the azimuth and elevation of
the source to be scanned. (We ignore sidereal motion for the sake of
this test, so they can be treated as absolute locations). The fourth
value is the flux density, a radio astronomical unit of measure for
brightness of a source.
You're given the following facts:
- an antenna can rotate at 40 degrees per minute
- an antenna can ascend or descend at 20 degrees per minute
- target scans take 5 minutes, calibration scans take 2 minutes
- variable-length scans take -2 * (flux density) + 20.5 minutes
The final output is to be a report. There is to be one line for each
scan, something like this:
#19: V 10.540 0.040 10.500
#20: C 2.045 0.045 2.000
#21: T 5.040 0.040 5.000
#22: C 2.040 0.040 2.000
So you have just the scan index, the total time of this scan, the "slew
time" (time it took the antenna to move into position) and the
on-source time. The last line of the report is aggregate information:
164.128 4.428 159.700
This is the total time, total slew time and total on-source time for
the whole file.
I've attached a sample input and output for this problem if you'd like
to take a crack at it. I had come up with the following parts, which
probably are too bulky for seasoned J users, but here they are:
NB. Geometry
diff =: -`(-~) @. <
minRotationDistance =: - <. &: (360&|) -~
NB. Antenna simulation
timeToRotate =: (%&40) @: minRotationDistance
timeToAscend =: (%&20) @: diff
Thanks for your patience! I appreciate all the help,
--
Daniel Lyons
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