gibson:teaching:fall-2014:math445:lab3
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| - | ====== Math 445 Lab 3: Array operations and basic plotting ====== | + | ====== Math 445 Lab 3: graphical data analysis ====== |
| - | Helpful Matlab functions | + | For this lab you will deduce the functional relationship between variables in data sets using graphical analysis. |
| + | The data sets are given as // N x 2// matrices with //x// as the first column and //y// as the second. | ||
| + | For each data set, you will find a function //y(x)// that fits the data, using the following steps: | ||
| - | sum, any, all, linspace | + | - Cut & paste the data set to a text file with an appropriate name, e.g. ''earthquakes.asc'' for problem 1. |
| - | plot, semilogy, semilogx, xlabel, ylabel, legend, axis | + | - Load the dataset to Matlab with ''load''. |
| + | - Extract the two columns of the loaded data into two appropriately named vectors, e.g. //R// and //N// for problem 1. For the remaining generic instructions I'll use the names ''x'' and ''y''. | ||
| + | - Experiment with ''plot'', ''semilogy'', ''semilogx'', and ''loglog'' to determine the functional relationship between ''y'' and ''x''. | ||
| + | - Estimate the constants in the log-linear relationship graphically to determine the function. | ||
| + | - Plot the estimated function and the data together, and fine-tune your function by adjusting the constants until there is a good fit between the function and the data. | ||
| - | **Problem 1:** Write a Matlab expression that sums the first N of each series and evaluate it for N=100. | + | Once you have good fit between the data and the function, make a plot that shows |
| - | (a) 1 + 1/2 + 1/3 + 1/4 + ... \\ | + | * the data set's //y// versus //x// as red circles |
| - | (b) 1 + 1/2 + 1/4 + 1/8 + ... \\ | + | * your function //y(x)// as a solid blue line |
| - | %%(c)%% 1 + 1/3 + 1/9 + 1/27 + ...\\ | + | * a legend indicating the meaning of each plotting symbol |
| - | (d) 1/2 + 2/3 + 3/4 + 4/5 + ...\\ | + | * appropriate labels for each axis and a title |
| - | (e) 1/2 - 2/3 + 3/4 - 4/5 + ...\\ | + | |
| - | + | ||
| - | **Problems 2,3 and 4:** | + | |
| - | Test that your expression gives the right answer on a good set of test vectors. | + | |
| - | But please turn in just the general Matlab expression, not the tests. | + | |
| + | For each data set, turn in your plots and your estimate of the function //y(x)//. | ||
| - | **Problem 2:** Given vectors x,y of the same length, write expression that has value | + | **Problem 1: The distribution of earthquake magnitudes, by Moment Magnitude scale.** Big earthquakes are rare, and |
| - | true (1) if **each** component of x is greater than the corresponding | + | little earthquakes are frequent. In fact, there is a very clean empirical law that governs how many earthquakes of a |
| - | component of y, false otherwise. | + | given magnitude typically occur world-wide in a given year. Your job is to deduce that law from the following |
| + | historical data. | ||
| - | **Problem 3:** Given vectors x,y of the same length, write expression that has value | + | <code> |
| - | true (1) if **any** component of x is greater than the corresponding | + | % M N |
| - | component of y, false otherwise. | + | 8 2 |
| + | 7 18 | ||
| + | 6 120 | ||
| + | 5 800 | ||
| + | 4 6200 | ||
| + | 3 49000 | ||
| + | 2 365000 | ||
| + | 1 2920000 | ||
| + | </code> | ||
| - | **Problem 4:** Given vector x, write expression that has value true (1) if the elements of x | + | The first column is the [[http://en.wikipedia.org/wiki/Moment_magnitude_scale | moment magnitude]] //M//, and the second column is the number of earthquakes //N// of that magnitude that occur, on average, in a year. The last two entries are estimates, since it's impossible to detect every small earthquake around the world. The data are obtained from [[http://www.earthquake.ethz.ch/education/NDK/NDK|Earthquake Statistics and Earthquake Prediction Research]] by Stefan Wiemer, Institute of Geophysics, Zurich. |
| - | are sorted in increasing order (that is, if no element is less than the previous element) and | + | |
| - | false otherwise. | + | |
| - | **Problems 5-11:** Turn in the Matlab code and the figures. Always label the figures appropriately, using ''title'', ''xlabel'' and either ''ylabel'' or ''legend''. The figures should be titled "Problem 5", etc. Read ''help'' for the following functions and then experiment with them to see how they affect the plot. | + | Using Matlab plotting commands, deduce the form of the functional relationship //N(M)//. Estimate the constants in the relationship by estimating the slope and the //y//-intercept, and then fine-tuning by matching the plot of your estimate against the plot of the data. |
| - | clf | + | **Problem 2: The distribution of earthquake magnitudes, by energy.** The moment magnitude scale is logarithmic, in that an earthquake of magnitude //M+1// releases about 32 times energy than an earthquake of magnitude //M//. The following data |
| - | hold on | + | set gives the number //N// of earthquakes in a given year of energy //E// measured in Joules. |
| - | hold off | + | |
| - | figure | + | |
| - | grid | + | |
| - | xticks | + | |
| - | yticks | + | |
| - | + | ||
| - | **Problem 5:** Plot sin(x) versus x for 100 evenly space points in x from 0 to 2pi, using a solid blue line. | + | |
| - | + | ||
| - | **Problem 6:** Plot sin(x) in red, cos(x) in green, over same x as problem 5. Use 'legend' to indicate which function is shown in which color. | + | |
| - | + | ||
| - | **Problem 7:** Plot $y = 5x^2 - 4x - 3$ for 100 evenly space points in x from -2 to 2. Superimpose an x,y grid on the plot. | + | |
| - | + | ||
| - | **Problem 8:** Make a plot of the unit circle. Make sure it's closed --no gap! Hint: use ''linspace'' to specify a range of angles, then ''cos'' and ''sin'' to produce vectors of the x,y coordinates of points on the unit circle. | + | |
| - | + | ||
| - | **Problem 9:** Plot $10^{3x}$ for 100 points x evenly space between -2 and 5. Choose the most | + | |
| - | appropriate plotting function. Hint: it ain't ''plot''! | + | |
| - | + | ||
| - | **Problem 10:** Plot $3 x^5$ for 100 points x evenly space between 1 and 4. Choose the most | + | |
| - | appropriate plotting function. Again, it ain't ''plot''! | + | |
| - | + | ||
| - | **Problem 11:** Make a histogram of 1000 random numbers from a normal (Gaussian) distribution. | + | |
| + | <code> | ||
| + | % E N | ||
| + | 6e16 2 | ||
| + | 2e15 18 | ||
| + | 6e13 120 | ||
| + | 2e12 800 | ||
| + | 6e10 | ||
gibson/teaching/fall-2014/math445/lab3.txt · Last modified: 2014/09/15 12:05 by gibson
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