21. Vectorization - ENGR 101, Section 100, Fall 10...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
ENGR 101, Section 100, Fall 10 M. Wellman 1 Subarrays and Vectorization ENGR 101, Lecture 21: 29 Nov 10 Announcements Project 7 due Wed 1 Dec Try to get done early, to avoid MATLAB license contention Note on conversion to doubles Watch for Project 8 soon…
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
ENGR 101, Section 100, Fall 10 M. Wellman 2 Accessing Array Elements Parentheses denote index operator ( ) unlike C++, MATLAB indices start at 1 Example: b = [1.0 3.0 5.0 2.0 4.0 6.0 ] b(1,3) 5.0 b(2,2) = 12 b = [1.0 3.0 5.0 2.0 12.0 6.0 ] Vectors as Indices Specifying a vector index selects a subarray with elements corresponding to the indices in the vector If v is a vector with n elts, then x(v) is equivalent to: [x(v(1)), x(v(2)), …, x(v(n))] For example, given: x = [ 1 7 4 –1 13 ] x(3) 4 x([1 3 5]) [1 4 13]
Background image of page 2
ENGR 101, Section 100, Fall 10 M. Wellman 3 Vectors as Matrix Indices Can also use vector indices on matrices For example, given: x = [ 1 7 4 –1 13 ] M = [ x; x+1; x+2 ] M(1,[1 3 5]) [1 4 13] M([1 2],[1 3 5]) ? [1 4 13 2 5 14] Colon Operator in Indices Colon operator provides shortcut to define vectors, so can use in vector index For example, given: x = [ 1 7 4 –1 13 ] x(2:4) [7 4 -1] Keyword end denotes last element: x(3:end) [4 -1 13] Colon on its own selects all values M = [ x; x+1; x+2 ] M(2,:) [2 8 5 0 14] M(:,[2 4]) [7 -1 8 0 9 1 ]
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
ENGR 101, Section 100, Fall 10 M. Wellman 4 Assigning to Subarrays arr = [ 1:4; 5:8; 9:12 ] arr([1 3],1:2) = [ -4 -3; -2 -1 ] arr(:,[2 4]) = 0 3 5 7 11 -4 -2 0 0 0 0 0 0 Exercise: Which does not generate the matrix shown? -1 -1 0 0 0 0 0 -1 -1 0 0 0 0 0 0 0 3 3 3 0 0 0 0 3 3 3 0 0 0 0 0 0 0 -1 -1 0 0 0 0 0 -1 -1 A B C
Background image of page 4
ENGR 101, Section 100, Fall 10 M. Wellman 5 What does this Function Do? function vout = myFunc (vin) vout = vin; vout(1:2:end-1) = vin(2:2:end); vout(2:2:end) = vin(1:2:end-1); Iteration and Vectorization Explicit iteration constructs: while for Elt-by-elt operations on arrays can also effectively
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 15

21. Vectorization - ENGR 101, Section 100, Fall 10...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online