This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: 14:440:127 Introduction to Computers for Engineers Notes for Lecture 03 Rutgers University, Fall 2009 Instructor Blase E. Ur 1 Functions for Matrices and Vectors 1.1 Max, Min There are also functions to find the maximum and minimum values of a vector or matrix. These are the creatively named max and min functions. For vectors, they return a single scalar with the absolute maximum number. For matrices, they return the maximum or minimum number in each column . Thus, as with the sum and prod functions, to find the absolute largest number in a matrix M , you would use max(max(M)) . The max and min functions can also be used to identify the location of the maximum or minimum number inside a vector (or, with a little bit more trouble, a matrix). If you write a statement like [a,b] = max(V) , where a and b are names of variables and V is a vector, then a will contain the largest value and b will contain the location of that largest value inside the vector V. Note that [a,b] is essentially just a vector of two variables. Also note that if the largest value is found more than one time inside the vector, b will contain the first location where it is found. V = [ 5 7 6 1 2 ]; [a,b] = min(V) a = 1 % The smallest element is 1 b = 4 % 1 is the 4th element of V What if you wanted to find the row and column in which the maximum or minimum is located? We can use a bit of a trick, as in the example below. We could also use the find function, which youll hear about in a second. NOTE, ERROR from last weeks lecture notes FIXED in example below V = [ 5 7; 6 1; 2 3]; [smallC,rowsC] = min(V) smallC = [2 1] % The smallest element IN EACH COLUMN rowsC = [3 2] % The ROWs which contains the smallest elementS [smallO,column] = min(smallC) smallO = 1 % The overall smallest element column = 2 % The COLUMN containing the overall smallest element row = rowsC(column) % Column 2 contains the smallest overall element. % Check which ROW in Column 2 contains the smallest element. row = 2 1.2 Mean, Median The mean and median functions operate on vectors just as youd expect from statistics. The mean cal culates the average, the sum of the elements of a vector divided by the number of elements. The median identifies the middle number if the vector were to be ordered from smallest to largest element. 1 As with the other matrix functions, calculating the mean or median of a matrix calculates the mean or median of each column. Thus, to find the mean of a matrix M , use mean(mean(M)) . However, this wouldnt work for the median think about why! Instead, use median(M(:)) , which first converts the matrix M to a vector (by making a vector containing ALL of the elements) and then finding the me dian. NOTE, ERROR from the printed lecture notes FIXED for median(M(:)) in the above paragraph 1.3 Sort, Sortrows You can also sort the elements of a vector in ascending (smallest to largest) order by using the sort func tion. For matrices, the sort function sorts each column individually.function sorts each column individually....
View
Full
Document
This note was uploaded on 01/11/2010 for the course 440 127 taught by Professor Blase during the Fall '09 term at Rutgers.
 Fall '09
 blase

Click to edit the document details