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Define a formula with real or complex values based on its mathematical expression.

The formula can be used in a later command as a function/formula argument or evaluated with particular values of the variables.

In many applications, this formula can be tabulated for particular values using the CALC_FONC_INTERP [U4.32.01] command, which produces a function or function_c concept such as DEFI_FONCTION [U4.31.02] or DEFI_NAPPE [U4.31.03].