EGR 115 Introduction to Computing for Engineers MATLAB Basics 2: Sub-Arrays Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers

Lecture Outline Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers MATLAB Basics  Sub-Arrays  Displaying data Slide 2 of 10

MATLAB basics Sub-arrays: Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers A sub-array is a subset of a larger array >> a = [ ];  The sub-array a(2:4) is the array [2 8 5] o i.e., elements a(1,2), a(1,3), and a(1,4) – Or elements a(2), a(3), and a(4)  The sub-array a(2:2:5) is the array [3 5] o i.e., elements a(1,2) and a(1,4) – Since the array 2:2:5 is 2, 4 Answer: a(1), a(4), a(7) ERROR!!! What is the array a(1:3:9)? Slide 3 of 10

MATLAB basics Sub-arrays: Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers Considering 2D arrays >> M = [ ; ; ];  The sub-array M(:,3:5) corresponds to all rows and cols 3, 4, 5  We can also index from the “end” >> M(:,end) refers to the last column  We can reassign a sub-set of the array >> M(1:2, [3 4]) = zeros(2,2); An error will occur if the LHS & RHS sizes are different!! Slide 4 of 10

MATLAB basics Sub-arrays: Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers Some special predefined values  pi – … to 15 significant digits  1i – The square root of -1 i.e., an imaginary number  Inf – Result of dividing by zero, i.e. infinity  NaN – Not-a-Number (undefined result)  clock – date & time = [year, month, date, hr, min, sec.sec]  eps – smallest possible number in MATLAB o Machine dependent  ans – stores the result of the last calculation Slide 5 of 10

MATLAB basics Sub-arrays: Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers Quiz 2.2 on page 43 of textbook a)c(2,:) b)c(:, end) c)c(1:2, 2:end) d)c(6) e)c(4:end) f)c(1:2, 2:4) g)c([1 3], 2) h)c([2 2], [3 3]) Slide 6 of 10

MATLAB basics Displaying Data: Display format Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers Setting the Default Display Format -> Preferences  Or type in command window >> format … format_examples.m Slide 7 of 10

MATLAB basics Displaying Data: The “disp” and “fprint” functions Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers Using the “disp” function >> disp(pi) >> disp(['The value of pi = ', num2str(pi)]) The “fprintf” function (borrowed from the C-language)fprintf  Typical use: fprintf(format_spec, variable_list) Format (conversion char) Description %dDecimal notation %eExponential notation %fFixed-point notation %gMore compact notation (%f or %e) \nNew line Slide 8 of 10 Concatenate the strings

MATLAB basics Displaying Data: The “fprint” function Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers fprintf examples:  Compare effects of the various conversion chars >> fprintf('Compare: pi = %d pi = %e pi = %f pi = %g\n', pi, pi, pi, pi);  We can also control the field width and precision o Field width is the min number of total digits to be printed o Precision is the number of decimal places >> fprintf('Compare: pi = %5.0f pi = %5.3f pi %5.8f \n', pi, pi, pi); fprintf in MATLAB is NOT exactly the same as the original C-function!! Slide 9 of 10

Next Lecture Friday 05 Sept 2014 EGR 115 Introduction to Computing for Engineers Data files, Array Operations, and Some of the built in functions Slide 10 of 10