Ventana software support forum

.

[Edited on 11-16-2006 by nikvyas]

[Edited on 11-16-2006 by nikvyas]

Thanks a lot Bob and JJ - it was fairly obvious I suppose - it just takes a bit of practice to adapt the brain into working in Vensim mode. I now have another related query, I'm afraid. I've attached a model which shows aircraft under repair. "Repair Activities To Be performed" shows the n...

Thanks JJ - however the model is empty!

Hi JJ - I haven't explained it properly. I can put it another way. Say we have two outputs as follows: output 1 = 101110100110011 output 2 = 001111101011010 output 3 = output 1 + output 2 = 102221201121020 Now - we are only allowed to have a value of '1' in each time step. If we have a value of 2 in...

One thing that isn't clear from the above is that output 3 could be elongated if there are 1's at the same time step on output1 and output2. Once a sequence of 1's has started, it needs to be finished. For expample: output1 = 1111011000100000011 output2 = 111011110110000111 output3 = 111111111111111...

Thanks Bob - I fear you're right.

btw - my company has just placed an order for the first few copies of Vensim!

Hello again. I have another query I'm afraid. I have two outputs - output 1 and output2. output1 = 11000001100etc (random) output 2 = 11110001100 etc (random) What I want to do is as follows: We start off with output 1 and pulse consecutive 1's. As soon as we hit a zero, output 2 pulses consecutive ...

Thanks JJ and Bob. I've come up with the following: distribution = RANDOM EXPONENTIAL( 5e-005 , 20000 , 0 , 0.2 , 5555 ) batch = DELAY BATCH(distribution, 1, 0 , 0 , 0 , 0 ) Time period is 1 hour So, if the MTBF is 5, it means that the average per hour is 0.2. The batch function waits until 'distrib...

Thanks again JJ. However, what I actually wanted was as follows: Say the Mean Time Between Failures is 5. Using the exponential function might give us a failure at the following times (for instance): 3, 9, 11, 17, 18 etc etc. So whereas you have shown the number of failures per day, what I need is a...

Hello again. What I need in addition (sorry for wanting so much) is to know how I apply this distribution to the time axis. ie., if the finish time is 100, I need a number of failure pulses along the time axis - and these failure pulses come from the exponential distribution. I just need to explain ...

Thanks very much for your response jj. The failure rate will be constant over time, which is why I think the exponential distribution is the more valid. Up to this point, my models have assumed a constant MTBF (of 5) so it behaves like a metronome - that is, every 5 hours of usage, the device will e...

Thanks Bob. However, all of the literature I have read indicates an exponential distribution is the most effective and, unfortunately, my boss also wants me to use an exponential distribution.

Any assistance grayefully received.

Good morning. I was wondering if somebody could help me out with, what should be, a very simple question - but for some reason I've got a mental block. How do I apply the exponential distribution within Vensim in the following case: Time step = 1 hour Final Time = 100 hours MTBF (mean time between f...

Thanks Laujjl - I think you are correct. I may have to re-think my method.

Laujjl - apologies for the late response - I've been on a course. I don't understand your point about 'concrete' problems as opposed to 'generalities' because the principles are the important matter - not specifics. However, I will explain my problem a bit more. We have a training device that has a ...

Thanks Tony - I'll try this sometime in the next week or so and report back with the results.

Nik

Morning Laujjl Thanks for your response. However, I don't think that 8000 time steps is absurd, because it merely equates to 8000 hours (one year). As Vensim has the capability to have time steps of seconds, it would seem reasonable that Vensim expects its users to work in these short intervals so, ...

Hello again. I have a question that I'd be very grateful to have some advice on. I want a fixed number of pulses per month, pulsed in a random fashion throughout the month. I.e., we have 10 pulses per month, but these ten pulses can happen at any time in the month. Can somebody please help? Thanks.

Hello all (Bob?) I have set my time step to one hour and the time bound between 1 and 8760 (1 year) which I would have thought is reasonable. However, the table truncates at 8000 which is more than a little annoying if you want to analyse the results. Is there a way to increase the truncation cut-of...

Thanks Bob - but I still get error messages. I did what you suggested as follows: TrainingPlatform: DS, FTP, PTT, RCT, SFET and then added the following to the "test" box variable: test[TrainingPlatform]=DS TRAINING PATTERN Then using the add eq button: test[TrainingPlatform]=FTP TRAINING ...

Hello again. I have a problem when using subscripts - it doesn't work! I've defined a subscript [training platform] which contains a range of 5. I then have the following equation: test[training platform] = DS TRAINING PATTERN[Training Platform], FTD TRAINING PATTERN[Training Platform],PTT TRAINING ...

That's fantastic - exactly what I wanted Bob!

Thanks again.

[Edited on 7-5-2006 by nikvyas]

Almost there Bob :cool: What I actually want is as follows: Take your "input" above. If the TIME STEP=1(day), the "input" has a pulse of 1 at 3 days for 1 day, a pulse of 4 at 7 days for 1 day, a pulse of 2 at 17 days for 1 day etc. Now, what I want is to adjust the DURATION (len...

I think we have a bit of serious miscommunication here Bob ;) Could we please try again, as it is vital to my model to get this right. :( As opposed to your last post where you defined 'output pulse', my pulses are random pulses of height 1 and duration 1. So for instance, the output from 'output pu...

Hi Bob - I think the equations I have are robust enough - they have been tested fairly exhaustively - although I will certainly take your recommendations aboard. All I really wanted to know Bob, was with an already defined pulse train, is there any way to adjust the duration of the pulses, rather th...