(let ((vs (call-with-input-file fname
                (lambda (ip)
                   (let* ((raddeg (/ 45.0 (atan 1.0)))
                          (degrad (/ raddeg))
                          (alf1 (* degrad (/ 360.0 (* u NS1))))
                          (alfmax (* NS1 alf1))
                          (ndata 0)
                          (atol 1.0e-4)
                          (alfs (map (lambda (n) (list (max 0.0 (- (* n alf1) (* 0.5 alf1) atol)) 
                                                       (min alfmax (+ (* n alf1) (* 0.5 alf1) atol))))                                                              
                                     (iota (+ NS1 1))))
                          (vals (make-vector (* 2 NS1 nsteps u) 0.0)))
                      (let floop ((line (peek-char ip)) (idx 0))
                         (if (eof-object? line)
                             vals
                             (begin
                                (read-line ip)
                                (set! ndata (string->number (read-line ip)))
                                (do ((line1 (read-line ip) (read-line ip))) ((or (not (string? line1)) (string=? line1 "11502,all_nodal_force")) vals)
                                  (let* ((fs (split-string (nosp line1) '(#\,)))
                                         (nums (map string->number fs))
                                                   (x (list-ref nums 1))
                                         (y (list-ref nums 2))
                                                   (tol 1e-3)
                                         (alf2 (atan y x))
                                         (nn1  (position (lambda (d) (and (>= alf2 (car d)) (<= alf2 (cadr d)))) alfs))                                         
                                         (nn (if (= nn1 NS1) 0 nn1))
                                         (fact (if (= nn1 NS1) -1.0 1.0))
                                         (r (sqrt (+ (* x x) (* y y))))
                                         (idx3 (+ (* 2 nn) idx))
                                         (idx4 (+ idx3 1)))
                                    (if (<= (* 1000.0 r) rmax)
                                        (begin   
                                           (vector-set! vals idx3 (+ (vector-ref vals idx3) (* fact (list-ref nums 4))))
                                           (vector-set! vals idx4 (+ (vector-ref vals idx4) (* fact (list-ref nums 5)))))
                                        #f)))
                                (floop (peek-char ip) (+ idx (* 2 u NS1)))))))))))