Recursion in OM
Creating a Recursion
A recursive program can be designed putting the reference of a blue patch in its own editor - that is, putting a patch within itself .
Creating a recursion : a patch is dropped into its own editor.
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If this patch has inputs and outputs, they will also appear on the patch box, so that the patch can be “called from inside itself”.
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Infinite Calls / Termination
A termination condition is absolutely necessary in a recursive patch. Otherwise, a succession of infinite calls will be triggered at the evaluation.
Remind to save all your material before calling a recursive patch.
Internal Patch Recursion
Do not ever build recursive programs with internal - red - patches, or with OMLoop boxes. **A function has to be **global to apply within itself.
Example: Factorial Patch
This recursive patch implements a preliminary version of the factorial function. It is called inside itself and calculates fact(n) = n x fact(n-1).
This function has no termination condition. If it is called in its current state, it will never end.
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Termination :
- The n values passed recursively are strictly decreasing, since they are each time equal to n-1.
- Besides, we know that fact(1) = 1.
- Therefore, we will add a non recursive branch via omif, applying to cases where n = 1.
The resulting patch means : i f n = 1, then fact(n) = 1 else , fact(n) = n x fact(n-1)
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When omif is evaluated, it evaluates the = test.
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The = test returns “nil” if n ≠ 1. I t returns “t” if n = 1. This is the termination condition of the patch.
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- omif returns the value of its second input (1), if it gets “t”.
- omif triggers the evaluation of the boxes that are connected to its third input if n ≠ 1.
- The factorial of n is calculated by om-, the fact sub patch and om*.
- omif returns the value of its second input (1), if it gets “t”.
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Using Omif
References :
Contents :
- OpenMusic Documentation
- OM User Manual
- OpenMusic QuickStart