Thanasis Naskos / Elton

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PRISM Manual | ThePRISMLanguage / MultipleInitialStates 
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    <p><a class='wikilink' href='Main.html'>The PRISM Language</a> /
</p><h1>Multiple Initial States</h1>

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<p>Typically, a <a class='wikilink' href='ModulesAndVariables.html'>variable</a> declaration
specifies the initial value for that variable.
The <em>initial state</em> for the model is then defined by the initial value for all variables.
It is possible, however, to specify that a model has <em>multiple</em> initial states.
This is done using the <code><strong>init</strong>...<strong>endinit</strong></code> construct,
which can be placed anywhere in the file except within a module definition,
and removing any initial values from variable declarations.
Between the <code><strong>init</strong></code> and <code><strong>endinit</strong></code> keywords, there should be a
predicate over all the variables of the model.
Any state which satisfies this predicate is an initial state.
</p>
<p class='vspace'>Consider again <a class='wikilink' href='Example1.html'>Example 1</a>.
As it stands, there is a single initial state <code>(0,0)</code> (i.e.  <code>x=0</code> and <code>y=0</code>).
If we remove the <code><strong>init</strong> 0</code> part of both variable declarations
and add the following to the end of the file:
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  <div class='sourceblocktext'><div class="prism"><span class="prismkeyword">init</span> <span class="prismident">x</span>=<span class="prismnum">0</span> <span class="prismkeyword">endinit</span><br/>
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  <div class='sourceblocklink'><a href='http://prismmodelchecker.localhost/manual/ThePRISMLanguage/MultipleInitialStates?action=sourceblock&amp;num=1' type='text/plain'>[&#036;[Get Code]]</a></div>
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<p class='vspace'>there will be three initial states: <code>(0,0)</code>, <code>(0,1)</code> and <code>(0,2)</code>.
Similarly, we could instead add:
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  <div class='sourceblocktext'><div class="prism"><span class="prismkeyword">init</span> <span class="prismident">x</span>+<span class="prismident">y</span>=<span class="prismnum">1</span> <span class="prismkeyword">endinit</span><br/>
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  <div class='sourceblocklink'><a href='http://prismmodelchecker.localhost/manual/ThePRISMLanguage/MultipleInitialStates?action=sourceblock&amp;num=2' type='text/plain'>[&#036;[Get Code]]</a></div>
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<p class='vspace'>in which case there would be two initial states: <code>(0,1)</code> and <code>(1,0)</code>.
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