Ventana software support forum

Dear colleagues,

when trying to get variable values from an ongoing vensim simulation into a Delphi 5.0-coded application I can't make the function vensim_get_val() work. However, after simulation it's easy to access the same variables with vensim_get_data().

To be more precise, here are the relevant Delphi code fragments:



// global type and variable definitions

type
TSingleTimeline = array[1..2000] of Single;

var
SumSubstrateHeight: TSingleTimeLine;
timeval: TSingleTimeline;



// procedures

procedure A;
var result: Integer;
begin
result := vensim_command('SIMULATE>RUNNAME|Current');
result := vensim_command('MENU>RUN|O');
result := vensim_get_data('Current', 'Sum Substrate Height', 'Time',
@SumSubstrateHeight[1], @timeval[1], 2000);

end;


procedure B;
var result, i: Integer;
CurrentTime, CurrentValue: Single;

begin
result := vensim_command('SIMULATE>RUNNAME|Current');
result := vensim_start_simulation(1,0,1);
if result = 1 then begin
while result = 1 do begin
i := vensim_get_val('Time', @CurrentTime);
i := vensim_get_val('Sum Substrate Height', @CurrentValue);
result := vensim_continue_simulation(20);
end;
result := vensim_finish_simulation();
end;
end;



While procedure A works perfectly, procedure B fails completely. When coming into the while-loop for the first time vensim_get_val() returns 0. At the second time the computer hangs or reports an access violation message. Can anybody tell me where the mistake is in procedure B?

Greetings
Peter

Hi Peter,

It does not look like anything is wrong to me - though you might try making the values vectors of length 1 and passing the first element.

Are you using version 5.7a?

Hi Bob,

thanks for your quick reply. I tried and changed procedure B into this form:



procedure B;
var result, i: Integer;
CurrentTime, CurrentValue: array[1..1] of Single;

begin
result := vensim_command('SIMULATE>RUNNAME|Current');
result := vensim_start_simulation(1,0,1);
if result = 1 then begin
while result = 1 do begin
i := vensim_get_val('Time', @CurrentTime[1]);
i := vensim_get_val('Sum Substrate Height', @CurrentValue[1]);
result := vensim_continue_simulation(20);
end;
result := vensim_finish_simulation();
end;
end;


However, the problem remains the same. In detail, it looks like this: When I call procedure B without placing breakpoints in there, simulation starts, but Delphi/Windows quickly reports an access violation in module vendll32.dll. When I call procedure B after that again, I get a message dialog (Caption: 'Vensim Program Error') which reads 'sim/init_vec1' (I guess this is the consequence of the abnormally terminated simulation before?).
After deactivating the vensim_get_val() calls, procedure B produces a smooth simulation run.

I think, It can't be a flaw in the model itself. Started directly in the Vensim environment as well as called from procedure A it always behaves dutifully and numerically stable. There are no stochastical elements in it. Its main structure is a 20x20 two-dimensional array of levels which are interlinked vertically, horizontally, and diagonally by rates.

Do you have an idea what it could be? I can work with a procedure A-like construction, no problem, but in some cases I would be happier with something like procedure B.

Best greetings
Peter

P.S. I'm using Vensim Version 5.7a.

Hi Peter,

A couple of things to check.

First, check the declaration of vensim_get_val to be sure it is the same as it is for other - I just checked and it is declared far instead of stdcall in the sample that ships with Vensim - that might be the source of the problem.

Second, try running the procedure without the vensim_get_val calls then look at the resulting vdf file in regular Vensim to be sure it OK (assuming this works).

Hi Bob,

thanks a lot! Using the following declaration (with 'stdcall' instead of 'far') did the trick:

function vensim_get_val(varname:PChar; varvals: SinglePtr): Integer ; stdcall ; external 'vendll32.dll' ;

vensim_get_val() now works in both versions of procedure B.

Greetings
Peter