(simulink beginner) : cannot load a time series from workspace

Hi all,

I am trying to figure out how to make some simple things work in Simulink. For example I have a matlab function which computes the position of an object given it's previous position and its velocity, as follows:

function [xnew vnew] = miModel(x,v,dt)
    % x is the current position 
    % v is the current velocity

      xnew  = x + dt*velocity;   % xnew is the new position
      vnew  = v;                 % new velocity =v in this example
  end

I want to load the 'velocity' variable from workspace, using the 'FromWorkspace' block. I define the velocity variable in the required structure as follows:

velocity.time = [linspace(0,1,100)]'; % 100
velocity.signals.values = [0*ones(50,1); 1*ones(50,1)] ;
velocity.signals.dimensions = [1];

I construct my model as shown below..

or here for a fullsize image:

http://www.freeimagehosting.net/newuploads/zpov6.png

when I run the simulation, it does not read the values I provide;i.e., first 50 iterations with velocity 0, and the other 50 with velocity =1; Please note that I am using a simple model in 1-D (velocity and position on x-axis only). Also, since I am working in discrete time, I set my solver to 'discrete' with fixed step = 1;

Any ideas? Many thanks...from a simulink beginner M

Answer 1

[Azzi Abdelmalek]

how to set a variable from workspace

time=0:0.1:10
signal=sin(t)
variable=[time;signal]'

[Azzi Abdelmalek]

don't forget to set stopt time simulation to max(time)

[Azzi Abdelmalek]

have you set any sample time?

[N/A]

Even thought I solved the problem, .. I feel what you mention is important..

1) In 'configuration parameters' I do set the simulation time = 200
(is this what you mean by max(time) ?). If not , then how do we set that?

2) what do you mean by sample time?Sample time for what?  In 'configuration parameters' i set the fixed time step for the simulation  = 1;

Sorry for these simple questions .. but I am a simulink beginner.. Thanks Azzi

[Azzi Abdelmalek]

for 1) exactly, stop time= max(time)

for 2) since you are working with a signal from workspace, and defined a vector time t with fixed space

sample time=time(2)-time(1)

I suggest that you set in simulation parameter/solver a fixed step equal to your sample time and do the same in all your blocks

[Azzi Abdelmalek]

for inherited sample time=-1, then the solver step time can be variable

[N/A]

Hi Azzi, Thanks again for your replies (and patience!)

1. For 1) Thanks! I was not aware I could literally use 'max(time)' in stop time box.
2. For 2) I need a little bit more clarification; (please let me know if my understanding of what you suggest is not right) My reasoning is that my real data will be coming in at high frequency, and I do not want to have a step as short as the period of the data input rate. Therefore, if you look at the diagram I have above,as an input to my block I have a constant 'dt'; this is the simulation time of each block, which as you suggest should be the same as the Fixed-step size in the solver!

So for 2), to do it on every block, (if i understood correctly) I was wondering whether it is possible to have a 'global constant : dt', and each block should read from that global constant this fixed time-step (sampling time). Also as the fixed-step size in the solver I should put 'dt' ...

thanks again M

[Azzi Abdelmalek]

yes, since you are handling a discret process, it is better if you control the sample time. you have just to set all sample time blocks to ts, in workspace or m file you set ts= what you want.

Answer 2

[N/A]

OK: I spotted the problem :

I was using :

velocity.time = [linspace(0,1,100)]';

And my simulation time was from 0: 200 with a time step =1, which means it will use inputs at time 0,1,2... therefore all good!

Thanks Azzi for the response anyway.

M