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

By: Doug

Doug — Tue, 17 Feb 2009 16:09:00 +0000

Carly,

Switch/case can be used in functions or scripts.

The switch command can work on any variable, not just one put in by the user.

Doug

By: Carly

Carly — Mon, 16 Feb 2009 02:00:24 +0000

Do the switch/case commands go in the function file or the script file.

Is there a way to automatically do the switch command or do you have to ask the user to input the value that you want to switch.

By: Doug

Doug — Thu, 29 Jan 2009 20:52:20 +0000

I think instead of
if (x < y < z)

you want

if (x < y) & (y < z)

The first construct could be done with numbers like this:

>> 0 < 0.5 < 1

ans =

(I suspect you expected the statement to be true!)

Which has an implied parenthesis here:

(0 < 0.5) < 1

Since (0 < 0.5) evaluates to true (1) this means
1 < 1

Which evaluates to false (0)

Try my construct:

>> (0 < 0.5) & (0.5 < 1)

ans =

And I think you will get what you were expecting.

-Doug

By: Yuri

Yuri — Thu, 29 Jan 2009 11:40:13 +0000

I’ve got a question about this string. Before this is a whole m-script with the needed parameterinputs, and there is no problem with them. It’s this particular part, where i need to get the 2000>REwater>3000 to work. But I believe this is not a right command for a Matlab m-file. Do you know an alternative to get REwater be unknown when the Reynoldsnumber is larger than 2000 but less than 3000?
Thanks in advance!

REwater=(roowater*v*D)/etawater
if REwater3000
disp(’The liquid is turbulent’)
elseif 2000>REwater<3000
disp(’The liquid of water is unknown, laminair and turbulent’)
end

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