Stop forcing mathtext mode for all strings

[mtreinish]

Summary

In #4616 the gate title and labels were changed to always use
matplotlib's mathtext mode. [1] This was a breaking change and will result
in users having weirdly formatted names and labels. For example places in
qiskit itself set gate names like 'Controlled-Evolution^1_dg' which will
not get rendered as expected in mathtext mode. The documented behavior for
labels and gate names before was to rely on matplotlib's rendering
behavior to expliclictly add '$' to the label string for sections that
should be rendered in mathtext mode. For example, this behavior was ported
to the latex circuit drawer in #3224 so that users could take advantage
of the same flexibility in how text was rendered by the drawer. This
commit removes the forced addition of '$' around all the label strings
to go back to the expected behavior.

Details and comments

Fixes #4667

[1] https://matplotlib.org/3.2.2/tutorials/text/mathtext.html

[Cryoris]

Could we change the subscripts to be uppercase and also non-slanted? Looks a bit weird now that in Rx, the x is cursive. Also if we use uppercase it'll be the same as the new IQX (which will hopefully be out soon).

[mtreinish]

Could we change the subscripts to be uppercase and also non-slanted? Looks a bit weird now that in Rx, the x is cursive. Also if we use uppercase it'll be the same as the new IQX (which will hopefully be out soon).

Done in: ea4735e

[Cryoris]

Suggested change

	'initialize': '$|psi>$'
	'initialize': '$|\\psi\\rangle$'

[enavarro51]

I don't think this \\psi works with the default font. I get a 'Glyph missing from current font' message. If there's interest in replacing the psi with the Greek symbol, it can be done in unicode in python.
I believe this will work,

'initialize': '$|\U0001d713\\rangle$'

Here's the output

[mtreinish]

$\\psi\\rangle$ works fine on my system and I haven't changed the default fonts in mpl.

It is probably dependent on your system fonts, and is not a matplotlib issue.

[Cryoris]

It seems the spacing in the multi-Pauli rotations is off:

this is before:

[enavarro51]

@mtreinish @Cryoris The latex_to_text method leaves underscores in the output. That's why the multi-rotation Pauli's are wider above. The text width calc thinks there are 4 chars instead of 3. This code at line 268 will take care of it.

            nl_text = LatexNodes2Text().latex_to_text(text)
            if text[0] == '$':
                nl_text = nl_text.replace('_', '')

            f = 0 if fontsize == self._style.fs else 1
            sum_text = 0.0
            for c in nl_text:

It produces,

There is also an issue with the cu1 and zz gates with params appearing too wide and also negative params are coming out too wide. I'll take a look at these and leave a fix here sometime this weekend.

[enavarro51]

On the cu1/zz issue dropping the '$$' from line 760, gate_width = (self._get_text_width(tname + ' ()',
seemed to take care of it.

[enavarro51]

@mtreinish Don't know if you want to do this here or put in a separate issue. I was going through the textbook and found this,

qc = QuantumCircuit(1) # Create a quantum circuit with one qubit
initial_state = [0,1]   # Define initial_state as |1>
qc.initialize(initial_state, 0) # Apply initialisation operation to the 0th qubit
qc.draw()              # Let's view our circuit

There's a pretty simple fix. Around line 885 inside the 'initialize' section replace

                    self._multiqubit_gate(q_xy, fc=fc, ec=ec, gt=gt, sc=sc,
                                          text=gate_text, subtext=vec)

with

                    if len(q_xy) == 1:
                        self._gate(q_xy[0], fc=fc, ec=ec, gt=gt, sc=sc,
                                   text=gate_text, subtext=vec)
                    else:
                        self._multiqubit_gate(q_xy, fc=fc, ec=ec, gt=gt, sc=sc,
                                              text=gate_text, subtext=vec)

[1ucian0]

Until the bot gets back on its feet. Here is the link for the tests!

https://mybinder.org/v2/gh/mtreinish/qiskit-core/fix-mathtext-mode-mpl-drawer?urlpath=apps/test/ipynb/mpl_tester.ipynb

[Cryoris]

LGTM, I couldn't find any corner cases anymore!