fixed missing parentheses typo in function "beta"
I'm about 75% sure we're filling in a ROW of the Lambda operator, so this fixes the indices in the Lambda matrix
Fixed bug where Lambda matrix elements in boundary cases were being filled in within the angle loop.

Lambda elements only need to be filled in once, inside the depth loop but outside the angle loop.
Removed matrix import since we don't need it.
Added elements of Lambda_star at l=0.
added FIXME note about figuring out how to make Lambda_star non-singular