using level 1 S-function with simulink

Hi all,

I am modeling a separator model with pressure and water level as 2 variables. I first made an m-file(hamda.m) with ode23tb, which is working( 4 plots: pressure, water level, flow of liq output and flow of gas output. then I used an level 1 s-function( gabileh) applying the m-file(hamda.m) I created as fellow

function [sys,x0,str,ts,simStateCompliance]  = gabileh(t,x,u,flag,varargin)

%  M-File S-Function implementing 

QLi = u(1); Qgi = u(2); kv1 = u(3); kv2 = u(4);

switch flag,

     %%%%%%%%%%%%%%%%%%
   % Initialization %
   %%%%%%%%%%%%%%%%%%
 case 0,                                                
   [sys,x0,str,ts, simStateCompliance] = mdlInitializeSizes(t,x,u,flag);

   %%%%%%%%%%%%%%%
   % Derivatives %
   %%%%%%%%%%%%%%%

 case 1,                
   sys = mdlDerivatives(t,x,u,QLi,Qgi,kv1,kv2);

   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   % Update, Output, and Terminate %
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 case {2, 4, 9},                                                
    sys = []; % do nothing

   %%%%%%%%%%
  % Output %
  %%%%%%%%%%
  case 3
    sys = mdlOutputs(t,x,u); 

otherwise
  DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));
end

%
%===================================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%===================================================================================
%
function [sys, x0,str,ts] = mdlInitializeSizes

sizes = simsizes;
sizes.NumContStates  = 2;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = 4;
sizes.NumInputs      = 4;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

x0  = [];
str = [];
ts  = [0 0];  % continuous sample time: [period, offset]

% Specify the block simStateCompliance. The allowed values are:
%    'UnknownSimState', < The default setting; warn and assume DefaultSimState

simStateCompliance = 'UnknownSimState';

% end mdlInitializeSizes

%
%===================================================================================
% mdlDerivatives
%
%===================================================================================
%
function sys = mdlDerivatives(t,x,u,varargin)

QLi = u(1); Qgi = u(2); kv1 = u(3); kv2 = u(4);

sys = hamda(t,x,u);

% end mdlInitializeSizes  

%=============================================================================
% mdlOutputs
% Return the output vector for the S-function
%=============================================================================
%
function sys = mdlOutputs(t,x,u)
sys =Qgt;
sys =QLt;
sys = x;

% end mdlOutputs

when I used the level-1 s-function in a simulink with 4 inputs and 4 ouputs, I keep having the same error:

Error in 'seprig/M-file S-Function1' while executing M-File S-function 'gabileh', flag = 0 (initialize), at start of simulation. MATLAB error message:
Attempted to access u(1); index out of bounds because numel(u)=0.

please help, thanks in adavance

Answer 1

[Kaustubha Govind]

The inputs to the S-function are not available at the time that mdlInitializeSizes is called (u is an empty variable - you could set a breakpoint and verify that). If you think about it, the stage flag=0 is the setup stage, so no inputs are available at this point. So the line:

   QLi = u(1); Qgi = u(2); kv1 = u(3); kv2 = u(4);

errors out.

Move it under the "case 1" section, so it is executed only where available and required.

[Hassan]

Thanks Kastuba,

I tried and it gives this error:

Error in 'seprig/M-file S-Function1' while executing M-File S-function 'gabileh', flag = 0 (initialize), at start of simulation. MATLAB error message:

Too many input arguments.

thanhs

[Kaustubha Govind]

You function mdlInitializeSizes has no input arguments. Change:

[sys,x0,str,ts, simStateCompliance] = mdlInitializeSizes(t,x,u,flag);

to

[sys,x0,str,ts, simStateCompliance] = mdlInitializeSizes;

[Hassan]

Thanks Kastuba,

I have steel the same problem, even with the changes

function [sys,x0,str,ts] = gabileh(t,x,u,flag,varargin)

% M-File S-Function implementing

switch flag,

%%%%%%%%%%%%%%%%%%

% Initialization %

%%%%%%%%%%%%%%%%%%

case 0,

[sys,x0,str,ts] = mdlInitializeSizes(varargin{:});

%%%%%%%%%%%%%%%

% Derivatives %

%%%%%%%%%%%%%%%

case 1,

sys = mdlDerivatives(t,x,u,flag);

u(1)=QLi; u(2)=Qgi; u(3)=kv1; u(4)=kv2;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Update, Output, and Terminate %

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

case {2, 4, 9},

sys = []; % do nothing

%%%%%%%%%%

% Output %

%%%%%%%%%%

case 3

sys = mdlOutputs(t,x,u);

otherwise

DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));

end

%

%===================================================================================

% mdlInitializeSizes

% Return the sizes, initial conditions, and sample times for the S-function.

%===================================================================================

%

function [sys, x0,str,ts] = mdlInitializeSizes(varargin)

sizes = simsizes;

sizes.NumContStates = 2;

sizes.NumDiscStates = 0;

sizes.NumOutputs = 4;

sizes.NumInputs = 4;

sizes.DirFeedthrough = 1;

sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

x0 = [0,0];

str = [];

ts = [0 0]; % continuous sample time: [period, offset]

% end mdlInitializeSizes

%

%===================================================================================

% mdlDerivatives

%

%===================================================================================

%

function sys = mdlDerivatives(t,x,u,varargin)

sys = hamda(t,x,u);

% end mdlInitializeSizes

%=============================================================================

% mdlOutputs

% Return the output vector for the S-function

%=============================================================================

%

function sys = mdlOutputs(t,x,u)

sys(1,2) = hamda(t,x,u);

sys(3,4) = x;

% end mdlOutputs

Simulink error message:

Error in 'seprig/M-file S-Function1' while executing M-File S-function 'gabileh', flag = 3 (output), at time 0. MATLAB error message:

Too many input arguments.

Thanks for ur help

[Kaustubha Govind]

You should perhaps run "dbstop if all error" and then run the Simulink model so that MATLAB automatically stops when an error occurs. You can debug the source of the error.