Both Uses

however
in
Flowers for Algernon -- Short Story
(Edited)

I am sorry, however, that my own contribution to the field must rest upon the ashes of the work of two men I regard so highly.
p. 17.6 *

however = though (used to connect contrasting ideas)
…I will continue to record my thoughts in these progress reports. It is one of my few pleasures. However, by all indications, my own mental deterioration will be very rapid.
p. 18.3

Definitions:

(1) (however as in: However, complications may...)
though (or another expression that connects contrasting ideas)

Based on idea 1 we might not expect idea 2, but this is a way of saying that even though idea 1 exists, we still have idea 2. Synonyms include in spite of that, despite that, nevertheless, nonetheless, on the other hand, in contrast and but.
(2) (however as in: However much she tried...)
to whatever degree (regardless of how much; or whatever unspecified amount)
(3) (however as in: However you do it, get it done!)
in whatever way
(4) (meaning too rare to warrant focus)
Much more rarely (and arguably incorrectly), however can be used to intensify the word how, as when one says "However did you find her?" Grammarians would suggest using two words for that usage: "How ever did you find her?"