:term:`CFOUR_POINTS <CFOUR_POINTS (CFOUR)>`
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      Specifies either single (=1, or SINGLE) or double (=2, DOUBLE) sided numerical differentiation in the finite difference evaluation of the Hessian. Two-sided numerical differentiation is considerably more accurate than the single-sided method, and its use is strongly recommended for production work.

      * **Type**: string
      * **Possible Values**: SINGLE, DOUBLE
      * **Default**: DOUBLE