corrected nystrom_eig

fact.ml

@@ -199,7 +199,7 @@ struct
     let c = M.chol b2 in
     let f = M.triangular_solve c b1 in
     let u, sigma, _ = M.svd f in
-    let lambda = M.dot sigma sigma in
+    let lambda = M.mul sigma sigma in
     u, lambda