diag_ext                Internal function to generate diagonal matrices
                        with possibly an offset with possibly mirrored
                        diagonal
fredholm_solve          Solve a Fredholm equation of the first and
                        second kind
indexing                Internal function to convert (row,col) to
                        vector index
makeH                   Make H Matrix as in (Twomey 1963)
simpson                 Internal function to calculate integration
                        weights for Simpson's rule
smooth                  Internal function to smooth a vector of values
                        using two-point average
volterra_solve          Solve a Volterra equation of the first kind
volterra_solve2         Solve a Volterra equation of the second kind
