Equivalent ROBDD with different variable ordering

Question

In this question, one ROBDD is already given, what steps to follow to draw the equivalent ROBDD with variable ordering c<b<a?

Thanks in advance! 

Answer 1

There are several options. You could read the formula from the ROBDD (here ¬a∧¬c ∨ a∧b∧c ∨ a∧¬b∧¬c), and draw a new ROBDD of it from scratch. Or you can reuse the part of the ROBDD where the changed variable order makes no difference (the low-branch of the a-root), and just re-draw the (sub-)ROBDD for a = true. As this (sub-)ROBDD just represents a↔b, only the b- and c-nodes flip their labels.

Comments

The above mentioned alternative means to apply the swap operation that is described in the slides.

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I checked in the slide. Thanks.

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Can you please specify which slide number. I am not able to find it. Thank you.

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slide 71 of the BDD chapter

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Thank you :)