local ffi = require 'ffi'
local gsl = require 'gsl'
local gsl_check = require 'gsl-check'
local function eval(bs, x)
 local dof, ws = bs.dof, bs.ws
 local c = matrix.alloc(dof, 1)
 local v = gsl.gsl_matrix_column (c, 0)
 gsl_check(gsl.gsl_bspline_eval(x, v, ws))
 return c
end
local function model(bs, x)
 local dof, ws = bs.dof, bs.ws
 local n = matrix.dim(x)
 local m = matrix.alloc(n, dof)
 for j = 0, n-1 do
 local xj = gsl.gsl_matrix_get(x, j, 0)
 local v = gsl.gsl_matrix_row (m, j)
 gsl_check(gsl.gsl_bspline_eval(xj, v, ws))
 end
 return m
end
local mt = {
 __index = {eval= eval, model= model}
}
local function bspline(a, b, nbreak)
 local breaks
 local brk
 if type(a) ~= 'number' then
 breaks = type(a) == 'table' and matrix.vec(a) or a
 brk = gsl.gsl_matrix_column (breaks, 0)
 nbreak = #breaks
 end
 local k = 4
 local dof = nbreak + k - 2
 local ws = ffi.gc(gsl.gsl_bspline_alloc (k, nbreak), gsl.gsl_bspline_free)
 if breaks then
 gsl_check(gsl.gsl_bspline_knots (brk, ws))
 else
 gsl_check(gsl.gsl_bspline_knots_uniform (a, b, ws))
 end
 local bs = {dof= dof, ws= ws}
 setmetatable(bs, mt)
 return bs
end
return bspline
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