BFGS-method modified

Remark 1 Step 5 must still be specified. The matrix has been introduced to indicate that the matrix k is modified by a (low-rank) correction matrix. When step 5 is reset by a specific update formula, the quasi-Newton method is named after that update (for instance BFGS-method, DFP-method, Broyden-method,. ..). 

Techniques used to find global and local energy minima include sequential simplex, steepest descents, conjugate gradient and variants (BFGS), and the Newton and modified Newton methods (Newton-Raphson). 

Direct thiation with elementary sulfur has been reported. Imidazole rings can be thiated in good yield by this method Sulfides can be conveniently obtained from thiolic esters by reduction with LiAlH4 and a large excess of BFg-etherate A modified Willgerodt-Kindler reaction with enamines at low temp, has been published... 

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