Comments on: MATLAB Basics: ‘Switch case’ vs. ‘If elseif’

By: Rick Stauf

Rick Stauf — Tue, 29 Jul 2008 00:42:43 +0000

Never Mind, I found a more efficient way to do it. Instead of searching the time area I simply multiply the time by the delta time to acquire the index number in the array. Thanks for your web tutorials. They are very helpful.

By: Rick Stauf

Rick Stauf — Mon, 28 Jul 2008 23:07:45 +0000

Doug,

I’m looking for a GoTo function for Matlab. I have an efficient search routine that I like to use in a number of areas that requires GoTos. Is there anything like this in matlab procedures?

Thank you for your help,
Rick

By: Doug

Doug — Thu, 27 Mar 2008 13:32:02 +0000

Phillip,

You need this for your input statement:

n=input(’Please input the figure:’,’s’)

This interprets whatever is typed as a string. Without that switch, MATLAB is taking what you type and interpreting it and thus looks for a function called “triangle” or whatever and does not find it.

Doug

By: Phillip Diedrick

Phillip Diedrick — Thu, 27 Mar 2008 11:08:01 +0000

I want to use the switch/case for the following. I want to prompt the user to input one the following strings: triangle, square,pentagon or hexagon. Depending which figure you input the program will then calculate the sum of the interior angles of the figure using (n-2)(180). I tried the following and I’m prompted with an error message. Here is my code.
clear;
clc;
n=input(’Please input the figure:’)
switch n
case (’triangle’)
n=3;
sum=(n-3).*(180)
case (’square’)
n=4;
sum=(n-3).*(180)
case(’pentagon’)
n=5;
sum=(n-3).*(180)
case (’hexagon’)
n=6;
sum=(n-3).*(180)
end
Please could you assist me.
Thanks

By: Jon

Jon — Thu, 20 Mar 2008 23:57:19 +0000

Phil,

Thanks for that! Exactly what I was looking for. MATLAB help does kind of fail to explain how to use logicals with a switch statement.

Jon

By: Doug

Doug — Fri, 11 Jan 2008 16:40:49 +0000

Phil,

Excellent example. Thank you!

Doug

By: Phil

Phil — Fri, 11 Jan 2008 03:05:59 +0000

Doug,
I often see programmers rely on the ‘if elseif’ chain in order to determine if a variable (n) falls into one of several ranges. MATLAB help is not clear on how this is done using the switch statement, but it is possible by comparing the logical value true against each of the range evaluations…

n=80
switch logical(true)
case n>100, disp(’high’);
case n>50, disp(’moderate’);
case n>0, disp(’low’);
otherwise disp(’invalid’);
end;

Again, this is a much more elegant solution than the ‘if elseif’ alternative.

Phil.

By: Doug

Doug — Wed, 09 Jan 2008 16:59:17 +0000

Robert,

I tested, and it really depended on the number of iterations. For reasonable numbers of iterations it did not seem to matter. TIC TOC and the profiler can be a big help here.

When asked about these kinds of things, I often say “Just code it”, run the profiler and see where the problems are. There is no need to try and optimize one second off of this kind of statement when there is some calculation that take 300 seconds anyways. Write your code clean and maintainable, then modify the slow bits as they appear.

Doug

By: Robert McCormick

Robert McCormick — Mon, 07 Jan 2008 00:24:55 +0000

Ok thanks Doug for this, but which of if-else and switch-case is computationally more efficient??