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PHYCS 3730/6720 Lab Exercise

Reading and references:
**Answer file Mylab04.txt**.

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Exercise 1. Scatter plots

Exercise and data courtesy Benjamin Bromley.

A file **~p6720/examples/lcrs/lcrs.e_gax** contains a list
of galaxy data (v_r [km/s], theta [radians], phi [radians], Mag
[absolute magnitude in broad-band red light]) from the Las Campanas
Redshift Survey. As in Assignment 1, Ex. 3, treat the recession
velocity v_r as a radial coordinate, so that (v_r, theta, phi) are
standard spherical polar coordinates.

Use **gnuplot** to make a 2-D map of the galaxies in space, with
each galaxy represented by a single dot. Tip: in the file name
gnuplot doesn't understand the tilde abbreviation **~**, so
to read the file, you'll need to spell it out like this:
**/u/course/p6720/examples/lcrs/lcrs.e_gax**. The galaxies all lie
in a "survey volume" that is roughly shaped like two curved pizza
slices with their pointed-ends touching at the origin. Make a plot
with the **x** and **y** values as follows:

x = v_r*cos(phi)*sin(theta) and y = v_r*sin(phi)*sin(theta);

This transformation converts the data from spherical polar coordinates
to rectangular coordinates and projects onto the x-y plane. Label
both the axes of the map in these new coordinates to say "km/s". [Hint:
see the "set xlabel" command.] Choose the point size to be 0.05 so you
can see the detail in the scatter plot. Then set up gnuplot so that
it writes your plot to a postscript file called **gax.ps**.
Finally, put all the relevant gnuplot commands into a text file called
**gax.gpl** (you can use emacs or gnuplot's
**save** utility). The objective is to be able to create the
postscript file with the single command **gnuplot gax.gpl**. There
is no need to copy the data file to your accounts; use the absolute
path given above to reference the file.
In your answer file, give a copy of only your gpl source file, **gax.gpl**.

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Exercise 2. Histograms

Generate a histogram for a Gaussian normal distribution using the
course random deviate utility **normdist** and the histogramming
course utility **hist**. Generate a distribution with mean 5
and standard deviation 1. Do this with 1000 random points using
random number seed 373.
To generate the random numbers, just type **normdist**. You will be
prompted for the mean, st dev, number of values, and seed. To
generate the histogram with **hist**, you should pipe the output
from **normdist** into **hist**. Use the **-g** option to
generate a file suitable for input to gnuplot.

In your answer file, give the Unix command and any gnuplot commands
for generating the file to be plotted.

Then plot the file. Generate a Postscript output file and display it
with **gv**. (Don't hand in this file.)