Match make_trapezoid to Pulseq MATLAB output

[simonthalen]

Summary

This PR updates make_trapezoid(...) to match MATLAB Pulseq makeTrapezoid(...) for equivalent inputs.

The main behavioral fix is the area + duration path. PyPulseq previously calculated shortest timing first, rounded ramp times, and then solved the requested duration. MATLAB Pulseq first solves the quadratic amplitude for the requested area/duration, rounds the ramp time from that amplitude, and finally recalculates amplitude after raster rounding. That produces different ramp/flat timing and amplitude for the same input.

Problem

For the same nominal input:

system = pp.Opts(max_grad=100, grad_unit='mT/m', max_slew=100, slew_unit='T/m/s')
gx = pp.make_trapezoid(channel='x', area=250, duration=1e-3, system=system)

PyPulseq and Pulseq produces different trapezoids.

As PyPulseq is described as a translation of Pulseq, this is a bug.

What Changed

• Changes the area + duration branch to match Pulseq's quadratic solve plus post-raster amplitude recalculation.
• Derives the rasterized rise and fall times from the solved amplitude, using PyPulseq's existing rise-time helper.
• Keeps the existing make_trapezoid(...) API and all unrelated validation behavior unchanged.
• Adds a MATLAB reference regression test and updates the existing affected expectation.

Behavior Compatibility

This is a bug-fix change limited to area + duration when ramp times are not supplied. That path now returns MATLAB-compatible timing and amplitude; other input combinations retain their existing PyPulseq behavior.

Reference Output

The regression test anchors this Pulseq-compatible output:

amplitude=268817.20430107525
rise_time=7.000000000000001e-05
flat_time=0.0008600000000000001
fall_time=7.000000000000001e-05
area=250.0
flat_area=231.18279569892474

Testing

PYTHONPATH=src python -m pytest tests/test_make_trapezoid.py
11 passed

python -m ruff check src/pypulseq/make_trapezoid.py tests/test_make_trapezoid.py
All checks passed!