University of Alaska Fairbanks
Geophysical Institute

Beyond the Mouse 2010 - The geoscientist's computational chest.

Lab 2: Matlab, Variables

Lab slides

Logic prep (pdf)

Introduction

Today we want you to play with variables, relational and logical operators in Matlab. This is a basis to understand flow control later on. We give you a list of examples to play with and want you to explain the results Matlab gives you. I don't care which way you'll play around, but I expect the result to be a Matlab script file (ends in .m) similar to my template. Your resulting script file will contain one line or a block of lines I give below and then one or many disp statements that explain the code and the response Matlab gives. After the last disp call you will place a pause statement. This serves two functions: 1) It's easy for me to look through, 2) you have documentation in form of a script (you may wanna call it relop_doc.m)

Exercise 0: ans

Open Matlab, type help ans or doc ans and understand what the variable ans is.

Exercise I: Assignments and Comparisons

Open Matlab and type the following lines in the command window. Explain each of Matlab's responses to your input!

test_var == 1
test_var = 1
test_var == 1
test_var == 5


Now, let's try something fancy:

test_var == 'A'
test_var = 65
test_var == 'A'
test_var == 'MATLAB'


What's with that? Hint.

Now create a numerical vector that will answer the question:

>> test_var == 'MATLAB'


with:

ans =

1 1 1 1 1 1


(Hint: Try solving this with arithmetics rather than looking up values in a table.)

Exercise II: Relational Operators

Open Matlab and type doc relop or help relopin the command window and read up on relational operators in Matlab.

Now we have more input. i and j are special, predefined variables in Matlab; the imaginary unit sqrt(-1). Do you think this statement is true?

0 > i^2 && sqrt(-1) > j

Now explain this - what's going on with the alternating results for the xor statement?

0 > i^2
xor(ans,1)
xor(ans,1)
xor(ans,1)


In Matlab the elementwise logical operators &, |, and xor compare elements of arrays and vectors to each other. Reproduce the following results using two arrays and one logical operator:

ans = 0 1 1 1
ans = 0 0 0 1
ans = 0 1 1 0


What are the answers to the deeper questions of life ... an why?

'2b' | ~'2b'
'MATLAB' == 'GMT'
'MATLAB' == 'GMT   '