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SBML Level 2 uses the MathML <csymbol> element to denote certain built-in mathematical entities without introducing reserved names into the model's component identifier namespace. The delay <csymbol> represents a delay function. The delay function has the form delay(x, d), taking two MathML expressions as arguments. Its value is the value of argument x at d time units before the current time. There are no restrictions on the form of x. The units of the d parameter are determined from the overall time units of the model. The value of the d parameter, when evaluated, must be numerical (i.e., a number in MathML real, integer, or "e-notation" format) and be greater than or equal to 0. The delay function is useful for representing biological processes having a delayed response, but where the detail of the processes and delay mechanism is not relevant to the operation of a given model.

The following example XML fragment encodes the equation k + delay(x, 0.1), or alternatively, kt + xt - 0.1:

<math xmlns=""> 
        <ci> k </ci> 
            <csymbol encoding="text" definitionURL=""> 
            <ci> x </ci>
            <ci> 0.1 </ci>

In SBML, the encoding attribute of <csymbol> must be set to "text".

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This page was last modified 22:59, 8 July 2008.

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