SImple question about Simulink S function

Hello all

How in S function I can obtain:

U(t2)-U(t1)/t2-t1

U(t2) is the velocity at current time step and U(t1) is the velcity at previous time step

Please guide

Regards

[Sameer]

Basically objective is to obtain the step size used during the particular iteration. Please guide!!!

Regards

Answer 1

[Kaustubha Govind]

You can use block.CurrentTime to get the current time in the S-function. You can use a DWork to store the current time at each step and use it in the next step to compute the difference.

[Sameer]

Thank you very much. I am trying to do but not getting success. Can you please clear it with an example....

Regards

[Kaustubha Govind]

Type msfcndemo_sfundsc2 at your MATLAB prompt to see an example S-function that uses a DWork to store the previous input value. You will need two Dworks, one for the input and one for current-time.

[Sameer]

Hello....Thank you for letting me know. I tried to write the s function though its running but I guess something is wrong in time,not sure though. Can you have a look and let me know whether I did it in the right manner or not.

    function msfcn_equation_trans(block)

    setup(block);

%endfunction

function setup(block)

   block.NumDialogPrms = 2;

    %%Register number of input and output ports
    block.NumInputPorts  = 1;
    block.NumOutputPorts = 1;

    %%Setup functional port properties to dynamically
    %%inherited.
    block.SetPreCompInpPortInfoToDynamic;
    block.SetPreCompOutPortInfoToDynamic;

    block.InputPort(1).DirectFeedthrough = false;
    %block.InputPort(2).DirectFeedthrough = false;

    %%Set block sample time to inherited
    block.SampleTimes = [-1 0];

    %%Set the block simStateCompliance to default (i.e., same as a built-in block)
    block.SimStateCompliance = 'DefaultSimState';

     %%Run accelerator on TLC
    block.SetAccelRunOnTLC(true);

    %%Register methods
    block.RegBlockMethod('SetInputPortDimensions', @SetInpPortDims);
    block.RegBlockMethod('PostPropagationSetup',    @DoPostPropSetup);
    block.RegBlockMethod('InitializeConditions',    @InitConditions);  
    block.RegBlockMethod('Outputs',                 @Output);  
    %block.RegBlockMethod('Update',                  @Update);  

%endfunction

function DoPostPropSetup(block)

    %%Setup Dwork
     block.NumDworks = 2;
     block.Dwork(1).Name = 'Intial'; 
     block.Dwork(1).Dimensions      = 3;
     block.Dwork(1).DatatypeID      = 0;
     block.Dwork(1).Complexity      = 'Real';
     block.Dwork(1).UsedAsDiscState = true;

    block.Dwork(2).Name = 'time'; 
    block.Dwork(2).Dimensions      = 1;
    block.Dwork(2).DatatypeID      = 0;
    block.Dwork(2).Complexity      = 'Real';
    block.Dwork(2).UsedAsDiscState = true;

%endfunction

function InitConditions(block)

    %%Initialize Dwork
    block.Dwork(1).Data = block.DialogPrm(2).Data;
    block.Dwork(2).Data=block.DialogPrm(1).Data;

%endfunction
function SetInpPortDims(block, idx, di)
    block.InputPort(idx).Dimensions = di;
    block.OutputPort(1).Dimensions = di*4;

function Output(block)
TD=block.CurrentTime-block.Dwork(2).Data;
X=10*ones(4,1);
[F]=fsolve(@(X) hope(X,block.Dwork(1).Data,TD,10),X);
block.OutputPort(1).Data =F;

%endfunction

%function Update(block)
  block.Dwork(1).Data=block.OutputPort(1).Data(2:4);
  block.Dwork(2).Data = block.CurrentTime;

%endfunction

where hope is a function returning the 4 equations.

Hope to get further guidance.

Regards