Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Basic function in matlab

  1. Apr 3, 2009 #1
    Hi, sorry to ask this, i know its really simple. I tried to look online for help but i couldnt understand why i was going wrong.

    I have a function u = [0.25*s]/[0.005 + s]

    I put this in a .m file.

    I am going to use this by puting an initial value (so) in to find u. Then u is used in a differential equation to find a new s.

    but when i for example write, s=2 iget this message

    >> s=2

    s =


    >> u
    ??? Input argument "s" is undefined.

    Error in ==> u at 2
    u = [0.25*s]/[0.005 + s]

    this is my m file

    function u = f(s)
    u = [0.25*s]/[0.005 + s]

    i havent really used mat lab before so any halp would be great.

    Thanks, rem
  2. jcsd
  3. Apr 3, 2009 #2
    Sorry, just figrued it out, i have to put in u(2)

    But does any one know how i know use this to put into a differentail equation (useing ODE45) to generate a new value for s. (which will b e used again in the differential)
  4. Apr 3, 2009 #3


    User Avatar
    Science Advisor

    You may want to take a look at the online documentation for how to structure arguments going into one of MATLAB's ODE solvers:

    Additionally, I've posted this before in this forum, but MATLAB scripts and functions (those are the m-files you posted previously):
    http://www.mathworks.com/access/helpdesk/help/techdoc/learn_matlab/f4-2525.html [Broken]

    If you're just starting out with MATLAB, I highly recommend book marking the MATLAB documentation webpage... It's more comprehensive and detailed than the built-in MATLAB documentation (which is decent for on-the-fly reference). If you wanted details about, say, the 'eye' function (identity matrix generator) you would just type in

    >> help eye
    Last edited by a moderator: May 4, 2017
  5. Apr 4, 2009 #4
    Thanks, the links you hav posted look very helpul.

    Than you :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook