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4.5 A string, yielding the numerical gradient if evaluated

Helptext:

c = cdiff (func,wrt,N,dfunc,stack,dx) - Code for num. differentiation
  = "function df = dfunc (var1,..,dvar,..,varN) .. endfunction

Returns a string of octave code that defines a function 'dfunc' that
returns the derivative of 'func' with respect to it's 'wrt'th
argument.

The derivatives are obtained by symmetric finite difference.

dfunc()'s return value is in the same format as that of  ndiff()

func  : string : name of the function to differentiate

wrt   : int    : position, in argument list, of the differentiation
                 variable.                                Default:1

N     : int    : total number of arguments taken by 'func'. 
                 If N=inf, dfunc will take variable argument list.
                                                        Default:wrt

dfunc : string : Name of the octave function that returns the
                  derivatives.                   Default:['d',func]

stack : string : Indicates whether 'func' accepts vertically
                 (stack="rstack") or horizontally (stack="cstack")
                 arguments. Any other string indicates that 'func'
                 does not allow stacking.                Default:''

dx    : real   : Step used in the symmetric difference scheme.
                                                 Default:10*sqrt(eps)

See also : ndiff, eval, todisk