The FAQ page

This page lists some of the most frequently asked questions about ENVI-met.

If you do have questions about ENVI-met, first look at the FORUM (Bulletin board)!
Maybe your question has been answerd before...

If NOT,.... make a new post in the forum!!!!
Questions that are mailed individually to us have a 90% chance of being IGNORD!

If you need it, we can offer you a professional support ranging from 1 month forum support up to a all-questions-answerd package.
Please e-mail me for a detailed offer!

Overview

Is ENVI-met different to other WINDOWS programs ?
Can I run ENVI-met in an virtualized environment under Mac OSX or Linux?
ENVI-met crashes, what can I do?
ENVI-met fails in producing a solution, I'm unhappy with this...
When the ENVI-met window was hidden by another window, it remains white and is only in areas redrawn when new outputs are posted....Why?
When I look at the CPU load, ENVI-met uses only 50% (25%,...) of my computer. Why?
Can I run more than one instance of ENVI-met ?
Can I distribute my ENVI-met run over several PCs or use more than one CPU in one computer?
Can I stop a model run and continue later ?
Why is there no "dynamic" version of ENVI-met that uses the memory resources as they are needed for my grid ?
Is it possible to predict the time needed for a simulation?
On which operating systems does ENVI-met run?
Is there a parallel or a 64Bit Version of ENVI-met?

Q&A in detail...

Is ENVI-met different to other WINDOWS programs ?

Answer Yes and No. On one hand, ENVI-met is a "normal" Windows program, on the other hand, it has system requirements that other programs don't have. You might experience trouble you don't have with other programs just because of bad resource management.

Also, ENVI-met constantly reads from and writes to the memory. Just one wrong value (e.g. a temperature of -9999 degree) can kill the whole simulation run. In other pieces of software you might only realize a short non-logical behavior...

ENVI-met will grab all the CPU power it can get. But it does not force Windows to give him all the CPU power, so you can switch to other applications if you have enough memory. On Windows NT systems, don't set ENVI-met to the highest priority because you won't be able to do anything after pressing the start button.

Can I run ENVI-met in an virtualized environment under Mac OS X or Linux?

Answer Theoretically yes, but it will be probably much to slow. Bettert make a dual boot on the Mac if you plan to run ENVI-met.

ENVI-met crashes, what can I do?

Answer Although these problems have reduced significantly since the first version was released in 1997, sometimes there might still be problems with the operating system itself. In general there are two kinds of crashes: System crashes and Program crashes.
Situations, in which ENVI-met fails to produce a solution but stops under controlled conditions are handled in the next section.

System crashes: There are at least 1.001 reasons why WINDOWS can crash. You can lower the chance of crashes by doing the following things:

• Start your simulation with a "fresh" system. Turn the power of and one before you start ENVI-met
• Close other programs, especially programs working in the background if you are low on memory
• If you calculate huge models, the best thing is to leave the computer and ENVI-met alone
• Do you have enough memory ? When WINDOWS starts swapping you are on the loosing path.... It might not crash the system but makes the simulation quite slow...
• Is your CPU-van o.k ? Don't forget that the processor might work for hours with a 100% load... that might cause thermal trouble.
• Disable your screen saver. (This saves calculation time)

ENVI-met crashes: Different to system crashes, this means that you get an error message on the screen.

Under some conditions ENVI-met produces nonsense running under WINDOWS. This results mainly in Errors in Floating point calculations when the initial turbulence field is calculated or other abnormal termination during the initialization. This problem can sometimes overcome by turning off the computer and reboot it and then restart ENVI-met. Also, there might be thermal problem with your CPU - you should check this.

Another reason might be bad memory modules - especially when the last Byte of physical memory is used you might experience trouble you normally won't get. In fact, a buggy memory module is of course always buggy, but in other programs you might not see the effect.

Some other things to check, if your configuration does not work:

• If ENVI-met crashes at the beginning, check the log-output. Probably some files are missing. Use the "Check only" option to generate a check output.
• Check if your input files and database files are ok. Especially check, if all entries are well formatted like in the original file. Make sure that all files only contain *plain ASCII* text like NOTEPAD produces. DO NOT write any file in a word processor (e.g. MS WORD) and save it as a normal document. This will produce unreadable formatted files
• Have you always used the point "." for your decimal numbers ? The comma "," is not a valid numeric operator !
• Is WINDOWS working properly ? ENVI-met allocates huge areas of memory for data storing. If a program has "gone wild" or WINDOWS has had some serious problems before or during the model run, it might have happened that the stored data are destroyed. Don't run ENVI-met if you are low on memory. Make sure that ENVI-met runs in your physical memory NOT in swapped memory !
• ENVI-met produces numerical errors like "Error in Floating Point Expression"... This is bad. Something went wrong. If you are sure that all input files have been read properly and only contain valid values, and there has not been any system problem running WINDOWS (see above) then there is a problem with your model configuration. Also see next section. Sorry, No general solution for this available. Please contact me.

ENVI-met fails in producing a solution, I'm unhappy with this...

Answer This can always happen to such a complex numerical like ENVI-met. We have invested a lot of time to increase the internal intelligence of ENVI-met. The recent version can handle a lot of trouble situations by itself and find a solution to ensure a proper model run. However, sometimes things simply don't work, and here are some clues what to do:

• Don't be sad or frustrated! Remember that you are working with a complex numerical model. 10 years ago this had required a million euros super-computer. Only because the computer you use was much cheaper, that does not mean that the program has become easier to handle. It's the other way round.
• Try to extend your model area via "Nesting Cells" if your have trouble with the flow.
• Move complex buildings away from the model border
• Extend the vertical extension of the model
• Decrease the time step if the model gets unstable in the normal calculation loop. (See [TIMESTEPS] section of the manual or online manual)
• Consider simplifying your model. It's not the real world either, so you can adjust some very complex corners to an easier configuration

Also, have a look at the warnings and information in the ENVI-met program output.
If your model is not working, send the input files (.in and .cf) to me ! I love to receive mails and also it helps to find bugs and improve the program !

When the ENVI-met window was hidden by another window, it remains white and is only in areas redrawn when new outputs are posted....Why?

Answer Although it looks messy, it is correct. ENVI-met does not react on any WINDOWS messages such as "Redraw yourself" during the simulation in order to save time. It restores the window from time to time.

When I look at the CPU load, ENVI-met uses only 50% (25%,...) of my computer. Why?

Answer: ENVI-met only uses one thread for the simulation (see next 2 FAQ's). Hence, if your system has more than one CPU (or a hyper-thread CPU), ENVI-met only uses one of the CPUs. Although this CPU is used a 100%, the overall usage is only 50% (or 25% if you have 4 CPUs) if the other CPU(s) is/are without tasks.

Can I run more than one instance of ENVI-met ?

Answer This is possible, but it is not clear if it is a good idea. If your computer has more than one CPU (or a strong CPU with hyper-threading) and a lot of memory, you can try do run more than one ENVI-met. You have to make your own mind if this more efficient than running just one version and do other things on the same PC.
IIf you have only one (classic) CPU, don't run more than one ENVI-met at a time. The programs will block each other and prevent an effective execution.

Can I distribute my ENVI-met run over several PCs or use more than one CPU in one computer?

Answer No. It is not very efficient to use a multi-threaded version of ENVI-met because it needs a constant data exchange between the processes. Also, the memory requirements will double as there will be one global data field for all processes and one local data field on which the single threads work on. In addition, a lot of synchronization and management overhead will be necessary. Therefore it is better to run more than one version of ENVI-met on the PC if you really want all of your CPUs to work...

Can I stop a model run and continue later ?

Answer This feature is not implemented at the moment. If you cancel your simulation, you have to start from the beginning.

Why is there no "dynamic" version of ENVI-met that uses the memory resources as they are needed for my grid ?

Answer Using dynamically dimensioned arrays might be ok for database applications, but it kills a numerical model because the access to the array elements is up to 10 times slower than if compiled static !

Is it possible to predict the time needed for a simulation?

Answer Not before actually running it, at least not from the program point of view. The factors influencing the model speed are too complex to be predicted. On the other hand, after ENVI-met has calculated a few hours model time, you can predict the remaining time by extrapolating the time needed for one hour of simulation time to the remaining hours.

On which operating systems does ENVI-met run ?

Answer

• WINDOWS VISTA: problems might occure, see the remarks on the download page
• WINDOWS 2000/XP: First choice, runs fine
• Everything below Windows 2000: I don't know. Actually, I don't care as well. Get yourself an up-to-date computer if you want to make numerical simulations ;)
• LINUX: Terminal version will be available for V4.0
• MAC OS X: Terminal version will be available for V4.0

Is there a parallel or a 64Bit Version of ENVI-met?

Answer Not at the moment. For the 64Bit version, there are not many things that would run better compared to the 32Bit version so this is more an academic kind of question.
On the other hand, seeing ENVI-met callenging the CPU only 50% on an duo-core or 25% on a quad core processor is a bit frustrating.
Unfortunately, things are not that easy to make a parallel version of ENVI-met. For the near future, I see no way for a parallel verision :((