Choose a function using a switch statement.

Hi, I am trying to create a switch function that will allow the user to choose to run one of two functions. Here is what I have :

function stressstrain
result = ...
    input('For Plane Stress press 1, for Plane Strain press 2 and then press enter \n');
switch result
case 1 
case 2  
otherwise disp 
    ('You pressed an unspecified key, please run again')
end
end

Is it possible to call and run a function using the case command ?

Apologies if this is a poorly worded and trivial question, I have only limited experience of matlab, but have an assignment due in very soon ! Thanks, Joshua

[per isakson]

Yes! Did you try?

[jo brown]

Yes, I tried ! But I'm a novice and have very limited experience of matlab.

Answer 1

[John D'Errico]

It looks like you are almost there, so here is an example of a switch construct that will call two different functions randomly.

switch round(rand(1))
  case 0
    x = cos(57);
  case 1
    x = sin(eps);
  otherwise
    % of course, we can't get into this otherwise branch
    % given the way I generated the switch argument, so I
    % could have left it out completely.
    disp('the sky is falling!')
end

[jo brown]

Nope, I don't get it :(

I have two variations of a function that I need to allow a user to call. Specifically, its the syntax after the case statement that I am not sure of.

I'll keep trying, but would appreciate any further help.

Answer 2

[jo brown]

I think I got it ! How does this look ?

function stressstrain
result = input('For Plane Stress press 1, for Plane Strain press 2 and then press enter \n');
switch result
case 1 
    run PStress
case 2
    run PStrain
otherwise disp ('You pressed an unspecified key, please run again')
end

[John D'Errico]

Assuming that PStress and PStrain are scripts, they need not use the run command.

Run is something that was built long ago, and really has no use anymore. Some like to use it to run scripts from the editor, but that is about all it has a use for anymore. So just use this:

function stressstrain
result = input('For Plane Stress press 1, for Plane Strain press 2 and then press enter \n');
switch result
case 1 
    PStress
case 2
    PStrain
otherwise disp ('You pressed an unspecified key, please run again')
end

[jo brown]

Hey John, thanks for your input. It seems to work either way, but I guess less code is better.

[John D'Errico]

Yep. Run works there, and will give the identical results, with or without. So I suppose I should test to see if there is a time cost for using run. Does run add extra overhead? Let us see...

I've created a simple script, that does essentially nothing interesting.

type testscript
a = 2;
b = a+3;

tic
for i = 1:100000
  testscript
end
toc

Elapsed time is 1.357657 seconds.

So 100000 calls to testscript took a bit over 1 second. Now I'll re-run the test using run in there.

tic
for i = 1:100000
  run testscript
end
toc
Elapsed time is 167.432911 seconds.

So there IS a significant cost to the use of run. Not truly massive per execution, taking roughly an extra 0.0017 seconds per execution of run.

(167.43 - 1.36)/100000
ans =
    0.0016607

A few CPU cycles here, a few there, and eventually it still all adds up to not that much, unless you will be using run a few millions of times.