Qiskit-terra: Pulse and Schedule plots do not start at t0=0

[taalexander]

Information

• Qiskit Terra version:
• Python version:
• Operating system:

What is the current behavior?

As noted in https://github.com/Qiskit/qiskit-terra/pull/3418#pullrequestreview-313349295, the pulse and schedule plots do not start at t=0, nor do they finish at t=t0+duration

Steps to reproduce the problem

import qiskit.pulse as pulse
import qiskit.pulse.pulse_lib as pulse_lib
sched = pulse.Schedule()
sched += pulse_lib.constant(10, 1.0)(pulse.DriveChannel(1))
sched.draw(channels_to_plot=[pulse.DriveChannel(1)])

What is the expected behavior?

They should start and stop at t0(duration)

Suggested solutions

Any ideas @nkanazawa1989?

[Matt-Stypulkoski]

I looked through the code a little more and it looks like it may be happening within the _draw_channels function. I tried playing around with the code in there, and if I have set the time array's first entry to 0, then the channel's figure correctly starts at 0. (Currently, time's first entry is 0.5, which is the amount of offset we see). I have not been able to reproduce the same fix for the end of the channel's figure though. Will play around with it a little more.

[nkanazawa1989]

@taalexander I think it is a problem of how to interpolate discrete pulse. As I remember, time shift of +0.5 indicates sampling at midpoint. i.e.

sample = [s0, s1, s2]
time = [t0, t1, t2, t3]

It should be noted that if you have sample pulse of duration 3, a length of time vector becomes 4 because it should start from 0, or t0. When visualizer interpolates this envelope, it resamples the above vectors to be [(t0+t1)/2, s0], [(t1+t2)/2, s1], [(t2+t3)/2, s2] - this is why your square pulse starts from 0.5, and ends at tf - 0.5.

If you remove the time shift, visualizer returns the figure exactly the same as _left_ sampling strategy and pulse ends at t2 in above example. This is confusing because pulse of duration 3 ends at t2.

[taalexander]

I don't think we should be interpolating by default (after all our pulses are discrete waveforms). What we should be plotting is [t0, t1, t1, t2, t2, t3] and [s0, s0, s1, s1, s2, s2]. If we want to interpolate on that, it would be fine.

[faraimazh]

Not because I have a sure fix but just to learn, may I come through and poke around until I find something. Good starting pointers welcome.

[nkanazawa1989]

@taalexander agreed. but cubic interpolation raises an error with that vectors, ValueError: Expect x to be a 1-D sorted array_like.

[taalexander]

@faraimazh feel free to poke around and comment here if you have any questions!

[taalexander]

@nkanazawa1989 would either of the two solution work?

1. Use a switch statement to use the vectors above I mention if interpolation is off (which I think it should be by default).
2. Modify the vectors to be [t0, t1-epsilon, t1+epsilon, t2-epsilon, t2+epsilon, t3] and [s0, s0, s1, s1, s2, s2]

[nkanazawa1989]

1 looks easy. In default, visualizer uses linear interpolation instead of disabling.

[taalexander]

Ok, than. Option one it is :smile:!

[taalexander]

@faraimazh do you still plan to work on this?

[faraimazh]

Sure, no problem. If I make progress I will let you know.

On Wed., 8 Jan. 2020, 01:23 Thomas Alexander, [e-mail]
wrote:

@faraimazh https://github.com/faraimazh do you still plan to work on
this? Otherwise, I will reassign.

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[lcapelluto]

Hi @faraimazh, how is this going?

[faraimazh]

@lcapelluto thanks for checking. I am only starting to follow now. I had to read a bit on terra and OpenPulse. I am not there yet but ready to get my hands dirty. Excuse my noob-ness, where do I find the drawing function or visualization files?

[nkanazawa1989]

the files are here.
https://github.com/Qiskit/qiskit-terra/tree/master/qiskit/visualization/pulse

and interpolation code is here.
https://github.com/Qiskit/qiskit-terra/blob/ff6b94120520b5c27d6316088eafc90338a97914/qiskit/visualization/pulse/interpolation.py#L26-L49

good luck and I'm happy to help :)

[faraimazh]

the files are here.
https://github.com/Qiskit/qiskit-terra/tree/master/qiskit/visualization/pulse

and interpolation code is here.
https://github.com/Qiskit/qiskit-terra/blob/ff6b94120520b5c27d6316088eafc90338a97914/qiskit/visualization/pulse/interpolation.py#L26-L49

good luck and I'm happy to help :)

Thanks. I am on it.

[faraimazh]

After setting up my environment and all, when I run the code to reproduce the problem here is the error I get.

[faraimazh]

After setting up my environment and all, when I run the code to reproduce the problem here is the error I get.

Issue resolved. I had two folders for qiskit-terra and in one of them there was a corrupt file.