Discard()

[NedaABD]

Hello, I hope you are doing well. I wonder to know the exact function of discard() in example 2-4.

In the cheatsheet it is written:
qc.discard()
Removes a specified qubit from the QPU. Can be used as a method on the qc object or a QInt object. If called without an argument then discards all qubits associated with the parent object.

my question is why do we remove all qubits we just allocated?

[emipc]

I had the same question. In fact, if you remove this line, the example still works.

[machinelevel]

Hi Neda and Emi, thanks for your notes! You're correct... it looks like that was left in by me by mistake. As you say, it's harmless, but here's more info:

The qc.discard() and qc.nop() in QCEngine exist mainly for diagramming purposes. Discard turns the lines soft, and nop provides some space.

...so if we add this code after the reset:

qc.nop();
qc.write(0);
qc.nop();
qc.discard();
qc.nop();

...we can get an effect like this, where the lines are "discarded" (visibly deactivated but otherwise unaffected):

[machinelevel]

I've fixed it in the repo, so it should eventually reflect in the sample page.
Thank you!