Cubic_Spline replaced by Spline

[Manish J. Thapa]

Hi,

Cubic_Spline has been replaced by Spline in v5. 

This was the use case before:

Cubic_Spline(time_array[0], time_array[-1], f(time_array))

Where f is the function you want to interpolate.

How does it look with Spline now that Cubic_Spline is gone? I could not do that implementation with Spline since I cannot find how to call this Spline method. Any idea?

[Éric Giguère]

There are no equivalent stand alone class.

You could use scipy's CubicSpline instead.

Scipy's CubicSpline can be used as coefficient of QobjEvo:

These all create equivalent QobjEvo:

```

H = qutip.QobjEvo([H0, scipy.interpolate.CubicSpline(x, y, bc_type=bc_type)])
H = qutip.QobjEvo([H0, np.array(y)], tlist=x, boundary_conditions=bc_type)
H = H0 * qutip.coefficient(np.array(y), tlist=x, boundary_conditions=bc_type)

```

[Manish J. Thapa]

Hi,

Thanks for your answer. It helps me a bit.

but I get some another error:

../src/ABC/solver/mesolver.py:64: in solve
    res = qt.mesolve(
../../../opt/miniconda3/envs/abclib/python3.11/site-packages/qutip/solver/mesolve.py:131: in mesolve
    H = QobjEvo(H, args=args, tlist=tlist)
qutip/core/cy/qobjevo.pyx:223: in qutip.core.cy.qobjevo.QobjEvo.__init__
    ???
qutip/core/cy/qobjevo.pyx:272: in qutip.core.cy.qobjevo.QobjEvo._read_element
    ???
../../../opt/miniconda3/envs/abc/lib/python3.11/site-packages/qutip/core/coefficient.py:175: in coefficient
    return coefficient_builders[type_](base, **kwargs)
qutip/core/cy/coefficient.pyx:520: in qutip.core.cy.coefficient.InterCoefficient.from_PPoly
    ???
qutip/core/cy/coefficient.pyx:515: in qutip.core.cy.coefficient.InterCoefficient.restore
    ???

Any idea what this could be?

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[Éric Giguère]

The `y` passed to CubicSpline must be complex.

This is an oversight in QuTiP...

[Éric Giguère]

I made a quick patch (https://github.com/qutip/qutip/pull/2397). It should work in the next release.