Prolate spheroidal wave function

[DiamonDinoia]

@mreineck you mentioned in the past that by playing with the parameters of the spreading function it is possible to achieve more digits at the same width. Do you have a summary of your experiments that we can use as a reference?

On our side we are thinking on moving to: Prolate. More readings DMK.

The reason Prolate was not used in the past is because is expensive to evaluate at runtime. But this is not an issue anymore since we tabulate the function.