To increase the amount of information displayed by PRISM (in particular, to display lists of states and probability vectors), you can use the "Verbose output" option (activated with comand-line switch -verbose or -v). To display additional statistics about MTBDDs after model construction, use the "Extra MTBDD information" option (switch -extraddinfo) and, to view MTBDD sizes during the process of reachability, use option "Extra reachability information" (switch -extrareachinfo).
Sometimes, model checking of properties for MDPs requires fairness constraints to be taken into account.
See e.g. [BK98],[Bai98] for more information.
To enable the use of fairness constraints (for P operator properties), use the -fair switch.
By default, when constructing a model, PRISM checks that all probabilities and rates are within acceptable ranges (i.e. are between 0 and 1, or are non-negative, respectively). For DTMCs and MDPs, it also checks that the probabilities sum up to one for each command. These checks are often very useful for highlighting user modelling errors and it is strongly recommended that you keep them enabled, however if you need to disable them you can do so via option "do prob checks?" in the GUI or command-line switch -noprobchecks.
You can also change the level of precision used to check that probabilities sum to 1 using the option "Probability sum threshold" (or command-line switch -sumroundoff.
CUDD, the underlying BDD and MTBDD library used in PRISM has an upper memory limit.
By default, this limit is 204800 KB (200 MB).
If you are working on a machine with significantly more memory this and PRISM runs out of memory when model checking, this may help.
To set the limit (in KB) from the command-line, use the -cuddmaxmem val switch.
You can also change this setting in the GUI, but you will need to close and restart the GUI (saving the settings as you do) for this option to take effect.
The Java virtual machine (JVM) used to execute PRISM also has upper memory limits.
Sometimes this limit will be exceeded and you will see an error of the form java.lang.OutOfMemory.
To resolve this problem, you can increase this memory limit.
On Unix, Linux or Mac OS X platforms, this is done by setting the environment variable PRISM_JAVAMAXMEM, for example (under a tcsh shell):
or (under a bash shell):
This sets the maximum to 4GB.
If you are running PRISM on Windows you will have to do this manually by modifying the prism.bat or xprism.bat scripts.
To set the memory to 4GB, for example, add -Xmx4g to the list of arguments in the call to java or javaw at the end of the file.
If you get an error of the form java.lang.StackOverflowError, then you can try increasing the stack size.
On Unix, Linux or Mac OS X platforms, you can change the value of PRISM_JAVASTACKSIZE in the prism script
(but note that, if you are compiling PRISM from source, this file gets regenerated from a template in src/bin when you recompile).
On Windows, you can edit the call to java or javaw directly, adding e.g. -Xss32M.
By default, PRISM's probabilistic model checking algorithms use an initial precomputation step which uses graph-based techniques to efficient detect trivial cases where probabilities are 0 or 1. This can often result in improved performance and also reduce round-off errors. Occasionally, though, you may want to disable this step for efficiency (e.g. if you know that there are no/few such states and the precomputation process is slow). This can be done with the -nopre switch. You can also disable the individual algorithms for probability 0/1 using switches -noprob0 and -noprob1.