MATLAB Basics 8 conditionals if statements

Transcription

1 1 MATLAB Basics 8 conditionals if statements Anthony Rossiter University of Sheffield For a neat organisation of all videos and resources

2 Introduction 2 1. We have established that using script files for sequences of operations is useful. 2. Sometimes, the specific computation we want to do deps upon the outcome of a previous computation such decisions are denoted as conditional operations. 3. This resource gives an introduction to basic conditional operations that can be coded in MATLAB. The coding is largely intuitive and follows reasoning common to humans and thus is easy and transparent to code.

3 What is logic in programming? Many circumstances need decisions. The action a computer code takes may dep on a decision, for instance: 1. How big should the axis be? 2. Should I use algorithm 1 or algorithm 2? 3. Do I have enough information to solve this problem? 4. Has the user supplied a proper value or made a typo? 5. Etc. These slides look at how to incorporate decision making into code.

4 Common conditional operations 4 Equality comparisons (numbers). Greater than and less than comparisons. Yes/No (logical variables). Other logical operations (AND, OR, etc). Text comparisons. Membership tests. For a more complete list use: >> help ops HERE the focus is on the if statement.

5 Common numerical comparisons 5 The action deps upon whether a given variable is bigger or smaller than a set value: e.g. if too cold, turn on the heating. The action relies on two values being equal: e.g. if the two persons share a birthday, celebrate together. The action deps upon a multiple of numeric tests: e.g. if the date is in the summer and I have more than 30 spare cash, then I can buy that new swimsuit.

6 MATLAB commands for comparison 6 If a>b; CODE; ; [Alternate: if gt(a,b).. ] Action the CODE if the numerical value of a is greater than the numerical value of b. Otherwise, do nothing. If a<=b; CODE; ; [Alternate: if le(a,b).. ] Action the CODE if the numerical value of a is less than or equal to the numerical value of b. Otherwise, do nothing.

7 MATLAB commands for comparison If a==b strict equality [Alternate: if eq(a,b)] 7 If a>=b greater than or equal to [Alternate: ge(a,b)] If a<b less than [Alternate: if lt(a,b)]

8 Combining commands 8 MATLAB supports the logical operations of AND, OR, XOR, NOT AND: BOTH CONDITIONS MUST HOLD If (a==b)&(c>d); CODE; and(a==b,c>d) OR: Either condition may hold If (a==b) (c>d); CODE; or(a==b,c>d) XOR: one but not both conditions must hold NOT: condition must be false

9 9 LIVE DEMONSTRATIONS WITH MATLAB

10 matlab_basics8a.m 10 %%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%% %%% The if statement a=1;b=1; if a<b;disp('yes a is less than b'); if a>b;disp('yes a is greater than b'); if a==b;disp('a and b are the same'); %%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%

11 matlab_basics8b.m a=-1 if a >=2; answer='high'; elseif a>=1; answer='middle'; elseif a>=0; answer = 'low' else; answer='none' disp('***************'); disp([sprintf('a is %g',a),' ',answer]) disp('***************'); Sequentional CONDITIONALS using elseif 11

12 a=3.3;b=4.2; matlab_basics8c.m 12 if and(ge(a,b),le(a,1)); disp('a is greater than or equal to b and less than or equal 1'); if and(lt(a,b),gt(a,1)); disp('a is less than b and greater than 1'); Logical OPERATIONS if or((a<b),(b==2)); disp('either a is less than b or b=2');

13 matlab_basics8a.m 13 a=1.3;b=4.2; if a>2; if and(ge(a,b),le(a,3)); disp('a is greater than or equal to b and less than or equal 3'); if and(lt(a,b),gt(a,2.1)); disp('a is less than b and greater than 2.1'); elseif a<0; else disp('a is negative'); if b>5; disp('a is between 0 and 2 and b is greater than 5'); else disp('a is between 0 and 2 and b is less than 5'); NESTED CONDITIONALS

14 Conclusions Demonstrated the use of if elseif -- statements in MATLAB. 2. Primarily focussed here on numerical comparisons such as equality, greater or lesser. 3. It is possible to compare strings and matrices, but some care is needed then. The core principle is that CODE is implemented if and only if the conditional statement is satisfied.

15 For a neat organisation of all videos and resources Anthony Rossiter Department of Automatic Control and Systems Engineering University of Sheffield University of Sheffield This work is licensed under the Creative Commons Attribution 2.0 UK: England & Wales Licence. To view a copy of this licence, visit or s a letter to: Creative Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA. It should be noted that some of the materials contained within this resource are subject to third party rights and any copyright notices must remain with these materials in the event of reuse or repurposing. If there are third party images within the resource please do not remove or alter any of the copyright notices or website details shown below the image. (Please list details of the third party rights contained within this work. If you include your institutions logo on the cover please include reference to the fact that it is a trade mark and all copyright in that image is reserved.)