The following lecture and demonstration of scripts and functions illustrate the real power of Matlab and the opportunity to get it to do some work for you. You can create these files in the text editor. They should be saved with a .m extension, and then run by typing their name (and adding arguements in the case of functions), but without the .m at the end.

here is a simple script that will say Hello:

%simple script to say hello world hello.m fprintf('HELLO WORLD!\n');and how I ran it and the outcome:

>> hello HELLO WORLD!See below for a bit more on the function

Here is a script that will load the topography data for today's assignment and then plot it and make a movie of it slowly rotating.

Have a look at the handout from Chapter 4 of Mastering Matlab 5.

"When you use Matlab functions such as inv, abs, angle, and sqrt, matlab takes the variables that you pass it, computes the required results using your input, and then passes those results back to you. The commands evaluated by the function as well as any intermediate variables created by those commands are hidden. All you see is what goes in and what comes out (i.e., a function is a black box)."--p. 143 from Mastering Matlab 5.

function r = rads(degrees) %this function takes an input angle in degrees and converts it to %radians %JRA, 11.22.99 r = degrees * (pi/180);Here is some Matlab action associated with it:

>> ls ans = factor_of_safety.m rads.m >> help rads this function takes an input angle in degrees and converts it to radians >> rads(180) ans = 3.1416Important points about the rads function:

- Note that the first line always starts with the word function and the calling syntax and input and output variable.
- The first set of contiguous comment lines (beginning with %) are the help text for the function.
- Note that you have to be in the directory in which the function is or type its complete path or have the path to that directory added to your Matlab search path

Here are a couple of pretty useful commands that I have used in my functions:

>> fprintf('here is a number = %.3f (that was the formatting)\n',2.5) here is a number = 2.500 (that was the formatting)

The main points are that you put a formatted placeholder in the line (%.3f) which in this case says to format the number as a 3 decimal place floating point. The \n tells Matlab to start a new line. Note the newline and the formatting placeholder along with the text are in the quotes. Then the number follows and is placed where it should be. If you have more than one placeholder, Matlab puts the numbers in sequentially and you can actually evaluate an expression there:

>> fprintf('here is a number = %.3f (that was the formatting), and here is its half = %.\n',2.53f\n',2.5,2.5/2) here is a number = 2.500 (that was the formatting), and here is its half = 1.250

c' or c = cohesion of the material

rho rock is rock density

rho water is water density

theta is the dip angle of the failure surface

h is the vertical thickness of the slide mass

g is gravity

m is the fraction of saturated thickness such that m = 0 if the water table is just below the slide plane and m = 1 if the water table is at the ground surface.

phi is the angle of internal friction

FS > 1 => STABLE

FS < 1 => UNSTABLE

FS = 1 => CRITICAL

Here is a function that takes care of the calculation of the factor of safety for us.

Here is the help text:

>> help factor_of_safety fs = factor_of_safety(c, h, theta, prock,m, phi) this function calculates the factor of safety for an infinite slope stability problem. See Arrowsmith notes note that suggested units are in parenthesis below JRA November 22,1999 Variables: external c = cohesion (kg m^-1 s^-2) h = slide mass thickness (m) theta = slope angle in degrees prock = rock density (kg m^-3) m = fraction of saturated thickness (such that m = 0 if the water table is just below the slide surface and m = 1 if the water table is at the ground surface) (dimensionless) phi = angle of internal friction in degrees internal g = gravitational acceleration (m s^-2) pwater = water density (kg m^-3) driving = driving stresses resisting = resisting stressesHere are some calculations to go with it:

This one is just past critical

>> factor_of_safety(11900,6,10,2000,1,8) c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 1.000, phi = 8.000 ans = 0.9896Slope goes up, safety goes down:

>> factor_of_safety(11900,6,Diminish saturation, safety goes up:20,2000,1,8) c = 11900.000, h = 6.000,theta = 20.000, prock = 2000.000, m = 1.000, phi = 8.000 ans = 0.5076

>> factor_of_safety(11900,6,10,2000,Increase internal friction, safety goes up0.5,8) c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000,m = 0.500, phi = 8.000 ans = 1.1889

>> factor_of_safety(11900,6,10,2000,1,Now how about a few plots:16) c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 1.000,phi = 16. 000 ans = 1.4042

>> clear mm fss >> for i=0:0.1:1 fss = [fss factor_of_safety(11900,6,10,2000,i,8)]; mm = [mm i]; end Warning: Reference to uninitialized variable fss. c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.000, phi = 8.000 Warning: Reference to uninitialized variable mm. c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.100, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.200, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.300, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.400, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.500, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.600, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.700, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.800, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 0.900, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 1.000, phi = 8.000 >> plot(mm,fss,'k') >> title('Effect of increasing saturation on factor of safety') >> xlabel('saturation = m') >> ylabel('FS') >>

>> clear tt >> clear fss >> for i = 1:20 fss = [fss factor_of_safety(11900,6,i,2000,1,8)]; tt = [tt i]; end Warning: Reference to uninitialized variable fss. c = 11900.000, h = 6.000, theta = 1.000, prock = 2000.000, m = 1.000, phi = 8.000 Warning: Reference to uninitialized variable tt. c = 11900.000, h = 6.000, theta = 2.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 3.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 4.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 5.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 6.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 7.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 8.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 9.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 10.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 11.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 12.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 13.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 14.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 15.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 16.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 17.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 18.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 19.000, prock = 2000.000, m = 1.000, phi = 8.000 c = 11900.000, h = 6.000, theta = 20.000, prock = 2000.000, m = 1.000, phi = 8.000 >> clf >> plot(tt,fss,'k') >> title('Factor of safety versus failure slope angle') >> xlabel('theta') >> ylabel('FS')

Pages maintained by

Prof. Ramón Arrowsmith

Last modified November 23, 1999