Infinite default bandwidth for PartialInverseOperator

[jishnub]

This would help with

julia> C = Conversion(Chebyshev(), Ultraspherical(1));

julia> P = PartialInverseOperator(C);

julia> P * Fun(x->x^3, Ultraspherical(1))
Fun(Chebyshev(), [0.0, 0.75, 0.0, 0.25])

julia> P * Fun(x->x^3, Ultraspherical(1)) ≈ Fun(x->x^3, Chebyshev())
true

This is mildly breaking, as the bandwidth was defined to be finite, however the default value was not anything special, and was unlikely to be useful in real cases where one would have needed to specify the bandwidth anyway. The current choice is more useful, as it makes the operator an exact inverse by default.

[codecov]

Codecov Report

Patch coverage: 93.00% and project coverage change: -0.79 ⚠️

Comparison is base (2f401fa) 71.22% compared to head (04d0943) 70.44%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #477      +/-   ##
==========================================
- Coverage   71.22%   70.44%   -0.79%     
==========================================
  Files          80       81       +1     
  Lines        8331     8463     +132     
==========================================
+ Hits         5934     5962      +28     
- Misses       2397     2501     +104     

Impacted Files	Coverage Δ
src/ApproxFunBase.jl	84.00% <ø> (+0.66%)	⬆️
src/LinearAlgebra/blas.jl	77.77% <ø> (ø)
src/Spaces/Spaces.jl	63.52% <ø> (-3.53%)	⬇️
src/Spaces/SumSpace.jl	70.44% <33.33%> (+0.77%)	⬆️
src/Operators/banded/CalculusOperator.jl	75.40% <80.64%> (+0.84%)	⬆️
src/Operators/functionals/CalculusFunctional.jl	79.48% <86.66%> (+7.07%)	⬆️
src/eigen.jl	96.42% <96.42%> (ø)
src/show.jl	95.61% <97.56%> (+12.77%)	⬆️
src/Operators/Operator.jl	70.70% <100.00%> (+3.13%)	⬆️
src/Operators/banded/ConstantOperator.jl	80.00% <100.00%> (+1.68%)	⬆️
... and 3 more

... and 47 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.